Thinking of taking a vacation this summer? Maybe you want to distract yourself with a bit of light science fiction fun. How about a deadly alien life form harbored within our solar system? That’s what Nick Kanas presents in his scientific novel “The Ca…
Just when we thought we’d seen every amazing image and video sequence from Monday’s transit of Mercury, a new one surfaces that makes our jaw hit the floor.
Remember, Mercury is tiny a world, just 1.4 times the diameter of our Moon, at 4,880 kilometers across. At about 9″ arc seconds across during the transit, it took Mercury seven and a half hours to race across the 30′ (over 180 times the apparent size of Mercury as seen from the Earth) disk of the Sun.
The video has an ethereal three dimensional quality to it, as we seem to race along with the fleeting world. You can see the granulation in the dazzling solar photosphere whiz by in the background.
Big Bear Solar Observatory Telescope Engineer and Chief Observer Claude Plymate explains some of the technical aspects of the captured sequence:
Video used with permission of the BBSO.
The BBSO operation is supported by NJIT, US NSF AGS-1250818, and NASA
NNX13AG14G grants, and the NST operation is partly supported by the Korea
Astronomy and Space Science Institute and Seoul National University and by
the strategic priority research program of CAS with Grant No.
The post Watch Mercury Race Across the Sun, Courtesy of the Big Bear Solar Observatory appeared first on Universe Today.
On May 9, 2016, Mercury passed directly between the Sun and Earth. No one had a better view of the event than the space-based Solar Dynamics Observatory, as it had a completely unobstructed view of the entire seven-and-a-half-hour event! This composite image, above, of Mercury’s journey across the Sun was created with visible-light images from the Helioseismic and Magnetic Imager on SDO, and below is a wonderful video of the transit, as it includes views in several different wavelenths (and also some great soaring music sure to stir your soul).
Mercury transits of the Sun happen about 13 times each century, however the next one will occur in only about three and a half years, on November 11, 2019. But then it’s a long dry spell, as the following one won’t occur until November 13, 2032.
Make sure you check out the great gallery of Mercury transit images from around the world compiled by our David Dickinson.
The post Watch Mercury Transit the Sun in Multiple Wavelengths appeared first on Universe Today.
(Note: Awesome images are being added as they come in!)
It’s not every day you get to see a planet pass in front of the Sun.
But today, skywatchers worldwide got to see just that, as diminutive Mercury passed in front of the disk of the Sun as seen from the Earth. This was the first transit of Mercury across the face of the Sun since November 8th, 2006, and the last one until November 11th, 2019.
Public events worldwide put the unique spectacle on display. Transits of innermost Mercury are much more frequent than Venus, the only other planet that can cross between the Sun and the Earth. Venus transited the Sun for the second and last time for this century on June 5th-6th, 2012, not to do so again until 2117.
Unlike a transit of Earth-sized Venus, you needed safely-filtered optical assistance to see tiny Mercury today against the Sun. At about 9″ arc seconds in size, you could stack over 180 Mercury’s across the 30′ arc minute disk of the Sun.
Lots of live feeds came to the rescue of those of us with cloudy skies, including Slooh, NASA, and our good friends at the Virtual Telescope project.
As is customary, we thought we’d feature a running blog of all of the great images as they trickle in to us here at Universe Today, throughout the day. This is one of our favorite things to do, as we show off some of the unique images as they trickle in from the field. Watch this space, as we’ll most likely be dropping in new images today throughout the day through to tomorrow.
Unlike solar eclipses, which are only usually picked up by solar observing satellites in low Earth orbit, spacecraft with different vantage points in space tend to see transits of Venus and Mercury as well, albeit at slightly different times. We’re expecting to see images from the joint NASA/ESA SOHO mission located at the L1 sunward point, as well as NASA’s Solar Dynamics Observatory, JAXA’s Hinode, and ESA’s Proba-2, all in orbit around the Earth.
It’s amazing just how far the imaging tech has come, since the last transit of Mercury in 2006. Back then, Coronado hydrogen alpha ‘scopes were the ‘hot new thing’ to observe the Sun with. Today, folks projected and shared the Sun safely with the world via social media online… and folks heeded our admonishment to stay cool and hydrate, and no reports of heat stroke from solar observers were noted.
Transits of Mercury occur on average about 13 times per century. The first was observed by Pierre Gassendi on November 7th, 1631. And although they have more of a purely aesthetic appeal than scientific value these days, transits of Mercury and Venus in past centuries were vital to pegging down the distance to the Sun via measuring the solar parallax, which in turn gave the scale of the solar system some hard numerical values in terms of the distance from the Earth to the Sun. Today, we know the solar parallax is tiny at a value of about 8.8″, tinier than the disk of Mercury as seen against the Sun today.
Fun fact: a transit of Mercury as seen from space actually turns up in the 200- science fiction flick Sunshine… to our knowledge, a transit of Venus has yet to hit the big screen. We also made mention of Mercury transits and more unique astronomical events spanning space and time in our original scifi tale Exeligmos.
Ready for more transit weirdness? Journey to Mars in 2084, and you can witness a transit of the Earth, Moon AND the innermost Martian moon Phobos. Let’s see, by then I’ll be…
Looking further out, one can wonder just when Mercury and Venus will transit the Sun… at the same time. We came across an interesting paper this weekend on just this subject. Keep in mind, the paper notes that orbits of the planets become a bit uncertain the farther out in time you look. But mark your calendars, as the next simultaneous transit of both Venus and Mercury occurs on September 17th, 13,425 AD. And hey, journey to Antarctica on July 5th, 6,757 AD and you can also witness a transit of Mercury during a partial solar eclipse;
Did anyone manage to catch a transit of the International Space Station during the Mercury transit? There were two good opportunities across North America today at 15:42 to 15:50 UT and 17:16 to 17:24 UT… a unique opportunity!
Well, it looks like the skies over southern Spain are clearing… time to set up our solar projection rig and observe the 2016 transit of Mercury for ourselves. Be sure to check this space for updates, and send those pics in to Universe Today’s Flickr forum!
The post Images of Today’s Transit of Mercury From Around the World appeared first on Universe Today.
Simple choices can sometimes lead to dramatic turns of events in our lives. Before turning in for the night last night, I opened the front door for one last look at the night sky. A brighter-than-normal auroral arc arched over the northern horizon. Although no geomagnetic activity had been forecast, there was something about that arc that hinted of possibility.
It was 11:30 at the time, and it would have been easy to go to bed, but I figured one quick drive north for a better look couldn’t hurt. Ten minutes later the sky exploded. The arc subdivided into individual pillars of light that stretched by degrees until they reached the zenith and beyond. Rhythmic ripples of light – much like the regular beat of waves on a beach — pulsed upward through the display. You can’t see a chill going up your spine, but if you could, this is what it would look like.
Auroras can be caused by huge eruptions of subatomic particles from the Sun’s corona called CMEs or coronal mass ejections, but they can also be sparked by holes in the solar magnetic canopy. Coronal holes show up as blank regions in photos of the Sun taken in far ultraviolet and X-ray light. Bright magnetic loops restrain the constant leakage of electrons and protons from the Sun called the solar wind. But holes allow these particles to fly away into space at high speed. Last night’s aurora traces its origin back to one of these holes.
The subatomic particles in the gusty wind come bundled with their own magnetic field with a plus or positive pole and a minus or negative pole. Recall that an ordinary bar magnet also has a “+” and “-” pole, and that like poles repel and opposite poles attract. Earth likewise has magnetic poles which anchor a large bubble of magnetism around the planet called the magnetosphere.
Field lines in the magnetosphere — those invisible lines of magnetic force around every magnet — point toward the north pole. When the field lines in the solar wind also point north, there’s little interaction between the two, almost like two magnets repelling one another. But if the cloud’s lines of magnetic force point south, they can link directly into Earth’s magnetic field like two magnets snapping together. Particles, primarily electrons, stream willy-nilly at high speed down Earth’s magnetic field lines like a zillion firefighters zipping down fire poles. They crash directly into molecules and atoms of oxygen and nitrogen around 60-100 miles overhead, which absorb the energy and then release it moments later in bursts of green and red light.
So do great forces act on the tiniest of things to produce a vibrant display of northern lights. Last night’s show began at nightfall and lasted into dawn. Good news! The latest forecast calls for another round of aurora tonight from about 7 p.m. to 1 a.m. CDT (0-6 hours UT). Only minor G1 storming (K index =5) is expected, but that was last night’s expectation, too. Like the weather, the aurora can be tricky to pin down. Instead of a G1, we got a G3 or strong storm. No one’s complaining.
So if you’re looking for that perfect last minute Mother’s Day gift, take your mom to a place with a good view of the northern sky and start looking at the end of dusk for activity. Displays often begin with a low, “quiet” arc and amp up from there.
Aurora or not, tomorrow features a big event many of us have anticipated for years — the transit of Mercury. You’ll find everything you’ll need to know in this earlier story, but to recap, Mercury will cross directly in front of the Sun during the late morning-early evening for European observers and from around sunrise (or before) through late morning-early afternoon for skywatchers in the Americas. Because the planet is tiny and the Sun deadly bright, you’ll need a small telescope capped with a safe solar filter to watch the event. Remember, never look directly at the Sun at any time.
If you’re greeted with cloudy skies or live where the transit can’t be seen, be sure to check out astronomer Gianluca Masi’s live stream of the event. He’ll hook you up starting at 11:00 UT (6 a.m. CDT) tomorrow.
The table below includes the times across the major time zones in the continental U.S. for Monday May 9:
|Time Zone||Eastern (EDT)||Central (CDT)||Mountain (MDT)||Pacific (PDT)|
|Transit start||7:12 a.m.||6:12 a.m.||5:12 a.m.||Not visible|
|Mid-transit||10:57 a.m.||9:57 a.m.||8:57 a.m.||7:57 a.m.|
|Transit end||2:42 p.m.||1:42 p.m.||12:42 p.m.||11:42 a.m.|
The post Give Mom the Aurora Tonight / Mercury Transit Update appeared first on Universe Today.
Welcome back to another installment in the “Definitive Guide to Terraforming” series! We complete our tour of the Solar System with the planet Mercury. Someday, humans could make a home on this hostile planet, leading to the first Hermians!
The planet Mercury is an intensely hot place. As the nearest planet to our Sun, surface temperatures can get up to a scorching 700 K (427° C). Ah, but there’s a flip-side to that coin. Due to it having no atmosphere to speak of, Mercury only experiences intensely hot conditions on the side that is directly facing the Sun. On the nighttime side, temperatures drop to well below freezing, as low as 100 K (-173° C).
Due to its low orbital period and slow rate of rotation, the nighttime side remains in the dark for an extended period of time. What’s more, in the northern polar region, which is permanently shaded, conditions are cold enough that water is able to exist there in ice form. Because of this, and a few reasons besides, there are many who believe that humanity could colonize and even terraform parts of Mercury someday.
The Planet Mercury:
With a mean radius of 2440 km and a mass of 3.3022×1023 kg, Mercury is the smallest planet in our Solar System – equivalent in size to 0.38 Earths. And while it is smaller than the largest natural satellites in our system – such as Ganymede and Titan – it is more massive. In fact, Mercury’s density (at 5.427 g/cm3) is the second highest in the Solar System, only slightly less than Earth’s (5.515 g/cm3).
Mercury also has the most eccentric orbit of any planet in the Solar System. With an eccentricity of 0.205, its distance from the Sun ranges from 46 to 70 million km (29-43 million mi), and takes 87.969 Earth days to complete an orbit. But with an average orbital speed of 47.362 km/s, Mercury also takes 58.646 days to complete a single rotation. This means that it takes 176 Earth days for the sun to rise and set on Mercury, which is twice as long as a single Hermian year.
As one of the four terrestrial planets of the Solar System, Mercury is composed of approximately 70% metallic and 30% silicate material. Based on its density and size, a number of inferences can be made about its internal structure. For example, geologists estimate that Mercury’s core occupies about 42% of its volume, compared to Earth’s 17%.
The interior is believed to be composed of a molten iron which is surrounded by a 500 – 700 km mantle of silicate material. At the outermost layer is Mercury’s crust, which is believed to be 100 – 300 km thick. The surface is also marked by numerous narrow ridges that extend up to hundreds of kilometers in length. It is believed that these were formed as Mercury’s core and mantle cooled and contracted at a time when the crust had already solidified.
Mercury’s core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury was once a larger planet which was struck by a planetesimal that stripped away much of the original crust and mantle, leaving behind the core as a major component.
Another theory is that Mercury formed from the solar nebula before the Sun’s energy output had stabilized, and was twice its present mass. However, most of this mass was vaporized as the protosun contracted and exposed it to extreme temperatures. A third hypothesis is that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost and not gathered to form Mercury.
At a glance, Mercury looks similar to the Earth’s moon. It has a dry landscape pockmarked by asteroid impact craters and ancient lava flows. Combined with extensive plains, these indicate that the planet has been geologically inactive for billions of years. However, unlike the Moon and Mars, which have significant stretches of similar geology, Mercury’s surface appears much more jumbled.
The vast majority of Mercury’s surface is hostile to life, where temperatures gravitate between extremely hot and cold – i.e. 700 K (427 °C; 800 °F) 100 K (-173 °C; -280 °F). This is due to its proximity to the Sun, the almost total lack of an atmosphere, and its very slow rotation. However, at the poles, temperatures are consistently low -93 °C (-135 °F) due to it being permanently shadowed.
In 2012, NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) probe detected signs of water ice and organic molecules in Mercury’s northern polar region. For over twenty years, scientists had suspected that in this area, Mercury’s craters could contain ice that was most likely deposited by comets in the past. Radar signals appeared to confirm as much, but it took the MESSENGER mission to confirm it.
Scientists believe that Mercury’s southern pole may also have ice. All told, it is estimated that Mercury could hold between 100 billion to 1 trillion tons of water ice at both poles, and the ice could be up to 20 meters deep in places. In the north pole, this water is particularly concentrated in craters like the Tryggvadottir, Tolkien, Kandinsky, and Prokofiev craters – which measure between 31 to 112 km in diameter.
In addition, the MESSENGER mission also noted the presence of “hollows” on Mercury’s surface which appeared to reach underground. Similar to hollows observed on the Moon and Mars, these features could be indicative of lava tubes that were formed during Mercury’s volcanically-active past. In both of these cases, stable lava tubes are seen as a possible location for colonies that would be shielded from radiation, space, and other hazards.
While terraforming an entire planet like Mercury is not exactly practical, its subsurface geology, cratered surface, and orbital characteristics make colonizing and terraforming some parts of it attractive. For example, in the northern polar region, where permanently-shadowed craters house water ice and organic molecules, domed structures could be set up that would allow any atmosphere created within to be contained.
This is a variation on the “Shell Worlds” concept, which in turn is part of the larger concepts known as paraterraforming – where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment. Using this process, the northern craters could be enclosed within a dome, orbital mirrors could focus sunlight within the domes, and the water ice could be evaporated.
Through the process of photolysis, the water vapor could be converted into oxygen gas and hydrogen, the latter of which could either be harvested as fuel, or vented into space. Ammonia could also be introduced, most likely mined from the outer Solar System, and converted into nitrogen gas through the introduction of specific strains of bacteria – Nitrosomonas, Pseudomonas and Clostridium species – that would convert the ammonia into nitrites (NO²-) and then nitrogen gas.
Lava tubes on Mercury could similarly be colonized, with settlements built within stable ones. These areas would be naturally shielded to cosmic and solar radiation, extremes in temperature, and could be pressurized to create breathable atmospheres. In addition, at this depth, Mercury experiences far less in the way of temperature variations and would be warm enough to be habitable.
Mercury’s relative proximity to Earth makes it a good location for terraforming and colonization. On average, Mercury is 77 million km (48 million miles) from Earth. To put that distance in perspective, it took the Mariner 10 probe (which took a much more direct route than MESSENGER) took a little under five months to reach Mercury from Earth.
Colonies established on Mercury would also be in a good position to provide extensive minerals and solar power to other planets. As the second-densest planet in the Solar System, Mercury has an abundance of iron, nickel and silicate minerals that would be of use locally and elsewhere. Also, its proximity to the Sun means that solar operations, possibly in the form of space-based solar arrays, could harness abundant energy.
This energy could then be beamed to other worlds for local use. Solar wind also adds hydrogen and helium to the planet’s exosphere, while radioactive decay within its crust is an additional source of helium. These could also be mined to create hydrogen fuel and helium-3, both of which could be used to power fusion reactors both on and off-planet.
As a result, colonies on Mercury, thanks to the abundance of water ice, minerals and other elements, would likely be largely self-sufficient as well. Unlike other potential sites that would require the importation of vast amounts of resources, Mercury’s first wave of colonists (aka. Hermians) could begin to see to much of their own needs shortly after setting down.
As always, the prospect of terraforming Mercury presents several challenges, an addressing one requires that others be addressed simultaneously. Fortunately, compared to many other planets (or moons) in the Solar System, they are fewer in number. In short, the challenges come down to issues of distance, technology, resources and infrastructure, and natural hazards.
To address the first, travel to and from Mercury would still take a significant amount of time using existing technology. While closer than many other potential sites, several trips would need to be made by crewed spacecraft, construction ships and support craft, which would take time and cost quite a lot using existing technology. In addition, hauling resources from the outer Solar System would take on the order on decades using the conventional engines and spacecraft.
Which brings us to item two: technology. In order for ships to travel to and from the outer Solar System to procure ammonia and other volatiles in large quantities (and in a reasonable amount of time), they would need to be equipped with advanced propulsion systems to make the journey. This could take the form of Nuclear-Thermal Propulsion (NTP), Fusion-drive systems, or some other advanced concept. But thus far, no such drive systems exist, with some being decades or more away from feasibility.
As for the next item, resources and infrastructure, colonizing and paraterraforming Mercury would require plenty of both. To start, it would take an immense amount of minerals and other materials to construct domes large enough to encase any of Mercury’s polar craters. Building orbital mirrors would be similarly be taxing. And while these minerals could be harvested locally, the process would be very expensive.
Similarly, the technology behind space-based solar power is not even close to where it would need to be harvest energy from the Sun and beam it directly to Earth (or other locations across the Solar System). Here too, the technology needs to come a long way; and even after we have that worked out, creating such a network between Mercury and other planets would be very expensive.
At the same time, it would require a level of infrastructure that also does not yet exist. Aside from a large fleet of spacecraft to ferry colonists, settling Mercury would also require a significant amount of construction vessels and automated robots. We would also need a series of stations between Earth and Mercury to provide for refueling and resupply.
And last, any construction and settlement efforts would have to deal with the dangers of exposure to extreme heat and Solar radiation. While a colony in the northern polar region and within Mercury’s lava tubes would be shielded, labor crews and construction ships would have to risk working in extremely hazardous conditions in order to build them.
In the end, and compared to other terraforming ventures, the colonization and paraterrforming of Mercury does seems rather doable. While it would require a huge commitment in terms of resources, the creation of technology and infrastructure that does not yet exist, and some serious hazard pay for the work crews who would assemble the Hermian settlements, the advantages could be enough to justify such an undertaking.
A colonized Mercury would mean abundant minerals and energy for the rest of the Solar System. Having these resources at our fingertips would be intrinsic to creating a post-scarcity economy, and could speed the development of colonies and terraforming efforts elsewhere.
We have written many interesting articles about Mercury and terraforming here at Universe Today. Here’s The Planet Mercury, The Definitive Guide to Terraforming, How Do We Terraforming Mars?, How Do We Terraform Venus?, How Do We Terraform the Moon?, How Do We Terraform Jupiter’s Moons?, and How Do We Terraform Saturn’s Moons?
Astronomy Cast also has a good episode on the subject, Episode 49: Mercury
And if you like the videos, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Fans of Arthur C. Clarke may recall how in his novel, 2010: Odyssey Two (or the movie adaptation called 2010: The Year We Make Contact), an alien species turned Jupiter into a new star. In so doing, Jupiter’s moon Europa was permanently terraformed, as its icy surface melted, an atmosphere formed, and all the life living in the moon’s oceans began to emerge and thrive on the surface.
As we explained in a previous video (“Could Jupiter Become a Star“) turning Jupiter into a star is not exactly doable (not yet, anyway). However, there are several proposals on how we could go about transforming some of Jupiter’s moons in order to make them habitable by human beings. In short, it is possible that humans could terraform one of more of the Jovians to make it suitable for full-scale human settlement someday.
The Jovian Moons:
Within the Jupiter system, there are 67 confirmed moons of varying size, shape and composition. In honor of Jupiter’s namesake, they are sometimes collectively referred to as the Jovians. Of these, the four largest – Io, Europa, Ganymede and Callisto – are known as the Galileans (in honor of their founder, Galileo Galilei). These four moons are among the largest in the Solar System, with Ganymede being the largest of them all, and even larger than the planet Mercury.
In addition, three of these moons – Europa, Ganymede and Callisto – are all believed or known to have interior oceans at or near their core-mantle boundary. The presence of warm water oceans is not only considered an indication of potential life on these moons, but is also cited as a reason for possible human habitation.
Of the Galilean Moons, Io, Europa and Ganymede are all in orbital resonance with each other. Io has a 2:1 mean-motion orbital resonance with Europa and a 4:1 resonance with Ganymede, which means that it completes two orbits of Jupiter for every one orbit of Europa, and four orbits for every orbit Ganymede. This resonance helps maintain these moons’ orbital eccentricities, which in turn triggers tidal flexing their interiors.
Naturally, each moon presents its own share of advantages and disadvantages when it comes to exploration, settlement, and terraforming. Ultimately, these come down to the particular moon’s structure and composition, its proximity to Jupiter, the availability of water, and whether or not the moon in question is dominated by Jupiter’s powerful magnetic field.
The process of converting Jupiter’s Galilean moons is really quite simple. Basically, its all about leveraging the indigenous resources and the moons’ own interactions with Jupiter’s magnetic field to create a breathable atmosphere. The process would begin by heating the surface in order to sublimate the ice, a process which could involve orbital mirrors to focus sunlight onto the surface, nuclear detonators, or crashing comets/meteors into the surface.
Once the surface ice begins to melt, it would form dense clouds of water vapor and gaseous volatiles (such as carbon dioxide, methane and ammonia). These would in turn create a greenhouse effect, warming the surface even more, and triggering a process known as radiolysis (the dissociation of molecules through exposure to nuclear radiation).
Basically, the exposure of water vapor to Jupiter’s radiation would result in the creation of hydrogen and oxygen gas, the former of which would escape into space while the latter remained closer to the surface. This process already takes place around Europa, Ganymede and Callisto, and is responsible for their tenuous atmospheres (which contain oxygen gas).
And since ammonia is predominantly composed of nitrogen, it could be converted into nitrogen gas (N²) through the introduction of certain strains of bacteria. These would include members of the Nitrosomonas, Pseudomonas and Clostridium species, which would convert ammonia gas into nitrites (NO²-), and then nitrites into nitrogen gas. With nitrogen acting as a buffer gas, a nitrogen-oxygen atmosphere with sufficient air pressure to sustain humans could be created.
Another option falls under the heading of “paraterraforming” – a process where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment. In the case of the Jovians, this would involve building large “Shell Worlds” to encase them, keeping the atmospheres inside long enough to effect long-term changes.
Within this shell, Europa, Ganymede and Callisto could have their temperatures slowly raised, the water-vapor atmospheres could be exposed to ultra-violet radiation from internal UV lights, bacteria could then be introduced, and other elements added as needed. Such a shell would ensure that the process of creating of an atmosphere could be carefully controlled and none would be lost before the process was complete.
With a mean radius of 1821.6 ± 0.5 km, and an average distance (semi-major axis) of 421,700 km from Jupiter, Io is the innermost of the Galileans. Because of this, Io is completely enveloped by Jupiter’s powerful magnetic field, which also the surface is exposed to significant amounts of harmful radiation. In fact, Io receives an estimated 3,600 rem (36 Sv) of ionizing radiation per day, whereas living organisms here on Earth experience an average of 24 rem per year!
The moon has the shortest orbital period of any of the Galileans, taking roughly 42.5 hours to complete a single orbit around the gas giant. The moon’s 2:1 and 4:1 orbital resonance with Europa and Ganymede (see below) also contributes to its orbital eccentricity of 0.0041, which is the primary reason for Io’s geologic activity.
With a mean density of 3.528 ± 0.006 g/cm3, Io has the highest density of any moon in the Solar System, and is significantly denser than the other Galilean Moons. Composed primarily of silicate rock and iron, it is closer in bulk composition to the terrestrial planets than to other satellites in the outer Solar System, which are mostly composed of a mix of water ice and silicates.
Unlike its Jovian cousins, Io has no warm-water ocean beneath its surface. In fact, based on magnetic measurements and heat-flow observations, a magma ocean is believed to exist some 50 km below the surface, which itself is about 50 km thick and makes up 10% of the mantle. It is estimated that the temperature in the magma ocean reaches 1473 K (1200 °C/2192 °F).
The main source of internal heat that allows for this comes from tidal flexing, which is the result of Io’s orbital resonance with Europa and Ganymede. The friction or dissipation produced in Io’s interior due to this varying tidal pull creates significant tidal heating within Io’s interior, melting a significant amount of Io’s mantle and core.
This heat is also responsible for Io’s volcanic activity and its observed heat flow, and periodically causes lava to erupt up to 500 km (300 mi) into space. Consistently, the surface of is covered in smooth plains dotted with tall mountains, pits of various shapes and sizes, and volcanic lava flows. It’s colorful appearance (a combination of orange, yellow, green, white/grey, etc.) is also indicative of volcanic activity which has covered the surface in sulfuric and silicate compounds and leads to surface renewal.
Io contains little to no water, though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons. In fact, Io has the least amount of water of any known body in the Solar System, which is likely due to Jupiter being hot enough early in the evolution of the Solar System to drive volatile materials like water off its surface.
Taken together, all of this adds up to Io being a total non-starter when it comes to terraforming or settlement. The planet is far too hostile, far too dry, and far too volcanically active to ever be turned into something habitable!
Europa, by contrast, has a lot of appeal for proponents of terraforming. If Io could be characterized as hellish, lava-spewing place (and it certainly can!), then Europa would be calm, icy and watery by comparison. With a mean radius of about 1560 km and a mass of 4.7998 ×1022 kg, Europa is also slightly smaller than Earth’s Moon, which makes it the sixth-largest moon and fifteenth largest object in the Solar System.
It’s orbit is nearly circular, with a eccentricity of 0.09, and lies at an average distance of 670 900 km from Jupiter. The moon takes 3.55 Earth days to complete a single orbit around Jupiter, and is tidally locked with the planet (though some theories say that this may not be absolute). At this distance from Jupiter, Europa still experiences quite a bit of radiation, averaging about 540 rem per day.
Europa is significantly more dense than the other Galilean Moons (except for Io), which indicates that its interior is differentiated between a rock interior composed of silicate rock and a possible iron core. Above this rocky interior is layer of water ice that is estimated to be around 100 km (62 mi) thick, likely differentiated between a frozen upper crust and a liquid water ocean beneath.
If present, this ocean is likely a warm-water, salty ocean that contains organic molecules, is oxygenated, and heated by Europa’s geologically-active core. Given the combination of these factors, it is considered a strong possibility that organic life also exists in this ocean, possibly in microbial or even multi-celled form, most likely in environments similar to Earth’s deep-ocean hydrothermal vents.
Because of its abundant water, which comes in both liquid and solid form, Europa is a popular candidate for proponents of colonization and terraforming. Using nuclear devices, cometary impacts, or some other means to increase the surface temperature, Europa’s surface ice could be sublimated and form a massive atmosphere of water vapor.
This vapor would then undergo radiolysis due to exposure to Jupiter’s magnetic field, converting it into oxygen gas (which would stay close to the planet) and hydrogen that would escape into space. The resulting planet would be an ocean world, where floating settlements could be built that floated across the surface (due to oceans depths of ~100 km, they could not be anchored). Because Europa is tidally-locked, these colonies could move from the day-side to the night-side in order to create the illusion of a diurnal cycle.
Ganymede’s is the third most distant moon from Jupiter, and orbits at an average distance (semi-major axis) of 1,070,400 km – varying from 1,069,200 km at periapsis to at 1,071,600 km apoapsis. At this distance, it takes seven days and three hours to completes a single revolution. Like most known moons, Ganymede is tidally locked, with one side always facing toward the planet.
With a mean radius of 2634.1 ± 0.3 kilometers (the equivalent of 0.413 Earths), Ganymede is the largest moon in the Solar System, even larger than the planet Mercury. However, with a mass of 1.4819 x 10²³ kg (the equivalent of 0.025 Earths), it is only half as massive, which is due to its composition, which consists of water ice and silicate rock.
Ganymede is considered another possible candidate for human settlement – and even terraforming – for several reasons. For one, as Jupiter’s largest moon, Ganymede has a gravitational force of 1.428 m/s2 (the equivalent of 0.146 g) which is comparable to Earth’s Moon. Sufficient enough to limit the effects of muscle and bone degeneration, this lower gravity also means that the moon has a lower escape velocity – which means it would take considerably less fuel for rockets to take off from the surface.
What’s more, the presence of a magnetosphere means that colonists would be better shielded from cosmic radiation than on other bodies, and more shielded from Jupiter’s radiation than Europa or Io. All told, Ganymede receives about 8 rem of radiation per day – a significant reduction from Europa and Io, but still well above human tolerances.
The prevalence of water ice means that colonists could also produce breathable oxygen, their own drinking water, and would be able to synthesize rocket fuel. Like Europa, this could be done by heating up the surface through various means, sublimating the water ice, and allowing radiolysis to convert it into oxygen. Again, the result would be an ocean world, but one with significantly deeper oceans (~800 km).
And then there is the distinct possibility that Ganymede, like Europa, has an interior ocean due to the heat created by tidal flexing in its mantle. This heat could be transferred into the water via hydrothermal vents, which could provide the necessary heat and energy to sustain life. Combined with oxygenated water, life forms could exist at the core-mantle boundary in the form of extremophiles, much like on Europa.
Callisto is the outermost of the Galileans, orbiting Jupiter at an average distance (semi-major axis) of 1,882,700 km. With a mean radius of 2410.3 ± 1.5 km (0.378 Earths) and a mass of 1.0759 × 1023 kg (0.018 Earths), Callisto is the second largest of Jupiter’s moons (after Ganymede) and the third largest satellite in the solar system. It is similarly comparable in size to Mercury – being 99% as large – but due to its mixed composition, it has less than one-third of Mercury mass.
Compared to the other Galileans, Callisto presents numerous advantages as far as colonization is concerned. Much like the others, the moon has an abundant supply of water in the form of surface ice (but also possibly liquid water beneath the surface). But unlike the others, Callisto’s distance from Jupiter means that colonists would have far less to worry about in terms of radiation. In fact, with a surface exposure of about 0.01 rem a day, Callisto is well within human tolerances.
Much like Europa and Ganymede, and Saturn’s moons of Enceladus, Mimas, Dione, Titan, the possible existence of a subsurface ocean on Callisto has led many scientists to speculate about the possibility of life. This is particularly likely if the interior ocean is made up of salt-water, since halophiles (which thrive in high salt concentrations) could live there.
However, the environmental conditions necessary for life to appear (which include the presence of sufficient heat due to tidal flexing) are more likely on Europa and Ganymede. The main difference is the lack of contact between the rocky material and the interior ocean, as well as the lower heat flux in Callisto’s interior. In essence, while Callisto possesses the necessary pre-biotic chemistry to host life, it lacks the necessary energy.
Like Europa and Ganymede, the process of terraforming Callisto would involve heating up the surface in order to sublimate the surface ice and create an atmosphere, one which produces oxygen through radiolysis. The resulting world would be an ocean planet, but with oceans that reached to depths of between 130 and 350 km.
Okay, we’ve covered the potential methods and targets, which means its time for the bad news. To break it down, converting one or more of the Galileans into something habitable to humans presents many difficulties, some of which may prove to be insurmountable. These include, but are are not limited to:
- Natural Hazards
- Ethical Considerations
Basically, the Jovian system is pretty far from Earth. On average, the distance between Jupiter and Earth is 628,411,977 million km (4.2 AU), roughly four times the distance between the Earth and the Sun. To put that into perspective, it took the Voyager probes between 18 months and two years to reach Jupiter from Earth. Ships designed to haul human passengers (with enough supplies and equipment to sustain them) would be much larger and heavier, which would make the travel time even longer.
In addition, depending on the method used, transforming the surfaces of Europa, Ganymede, and/or Callisto could require harvesting comets and iceteroids from the edge of the Solar System, which is significantly farther. To put that in perspective, it took the New Horizons mission over eight years to reach Pluto and the Kuiper Belt. And since any mission to this region of space would need to haul back several tons of icy cargo, the wait time involved would be on the order of decades.
Ergo, any vessels transporting human crews to the Jovian system would likely have to rely on cryogenics or hibernation-related technology in order to be smaller, faster and more cost-effective. While this sort of technology is being investigated for crewed missions to Mars, it is still very much in the research and development phase.
As for transport missions to and from the Kuiper Belt, these ships could be automated, but would have to come equipped with advanced propulsion systems in order to make the trips in a decent amount of time. This could take the form of Nuclear-Thermal Propulsion (NTP), Fusion-drive systems, or some other advanced concept. So far, no such drive systems exist, with some being decades or more away from feasibility.
An alternative to this last item could be to harvest asteroids from near Earth, the Asteroid Belt, or Jupiter’s Trojans. However, this brings up the second aspect of this challenge, which is the problem of infrastructure. In order to mount multiple crewed missions to the Jovian system, as well as asteroid/iceteroid retrieval missions, a considerable amount of infrastructure would be needed that either does not exist or is severely lacking.
This includes having lots of spaceships, which would also need advanced propulsion systems. Just as important is the need for refueling and supply stations between Earth and the Jovian System – like an outpost on the Moon, a permanent base on Mars, and bases on Ceres and in the Asteroid Belt. Harvesting resources from the Kuiper Belt would require more outposts between Jupiter and most likely Pluto.
Where “Shell Worlds” are concerned, the challenge remains the same. Building an enveloping structure big enough for an entire moon – which range from 3121.6 km to 5262.4 km in diameter – would require massive amounts of material. While these could be harvested from the nearby Asteroid Belt, it would require thousands of ships and robot workers to mine, haul, and assemble the minerals into large enough shells.
Third, radiation would be a significant issue for humans living on Europa or Ganymede. As noted already, Earth organisms are exposed to an average of 24 rem per year, which works out to 0.0657 rem per day. An exposure of approximately 75 rems over a period of a few days is enough to cause radiation poisoning, while about 500 rems over a few days would be fatal. Of all the Galileans, only Callisto falls beneath this terminal limit.
As a result, any settlements established on Europa or Ganymede would require radiation shielding, even after the creation of viable atmospheres. This in turn would require large shields to be built in orbit of the moons (requiring another massive investment in resources), or would dictate that all settlements built on the surfaces include heavy radiation shielding.
On top of that, as the surfaces of Europa, Ganymede and Callisto (especially Callisto!) will attest, the Jovian system is frequented by space rocks. In fact, most of Jupiter’s satellites are asteroids it picked up as they sailed through the system. These satellites are lost on a regular basis, and new ones are added all the time. So colonists would naturally have to worry about space rocks slamming into their ocean world, causing massive waves and blotting out the sky with thick clouds of water vapor.
Fourth, the issue of sustainability, has to do with the fact that all of the Jovian moons either do not have a magnetosphere or, in the case of Ganymede, are not powerful enough to block the effects of Jupiter’s magnetic field. Because of this, any atmosphere created would be slowly stripped away, much as Mars’ atmosphere was slowly stripped away after it lost its magnetosphere about 4.3 billion years ago. In order to maintain the effects of terraforming, colonists would need to replenish the atmosphere over time.
Another aspect of sustainability, one which is often overlooked, has to do with the kinds of planets that would result from terraforming. While estimates vary, transforming Europa, Ganymede and Callisto would result in oceans that varied in depth – from 100 km (in the cae of Europa) to extreme depths of up to 800 km (in the case of Ganymede). In contrast, the greatest depth ever measured here on Earth was only about 10 km (6 miles) deep, in the Pacific’s Mariana Trench.
With oceans this deep, all settlements would have to take the form of floating cities that could not be anchored to solid ground. And in the case of Ganymede, the oceans would account for a considerable portion of the planet. What the physicals effects of this would be are hard to imagine. But it is a safe bet that they would result in tremendously high tides (at best) to water being lost to space.
And finally, there is the issue of the ethics of terraforming. If, as scientists currently suspect, there is in fact indigenous life on one or more of the Jovian moons, then the effects of terraforming could have severe consequences or them. For instance, if bacterial life forms exist on the underside of Europa’s icy surface, then melting it would mean death for these organisms, since it would remove their only source of protection from radiation.
Life forms that exist close to the core-mantle boundary, most likely around hydrothermal vents, would be less effected by the presence of humans on the surface. However, any changes to the ec0logical balance could lead to a chain reaction that would destroy the natural life cycle. And the presence of organisms introduced by humans (i.e. germs), could have a similarly devastating effect.
So basically, if we choose to alter the natural environment of one or more of the Jovian moons, we will effectively be risking the annihilation of any indigenous life forms. Such an act would be tantamount to genocide (or xenocide, as the case may be), and exposure to alien organisms would surely pose health risks for human colonists as well.
All in all, it appears that terraforming the outer Solar System might be a bit of a non-starter. While the prospect of doing it is certainly exciting, and presents many interesting opportunities, the challenges involved do seem to add up. For starters, it doesn’t seem likely or practical for us to contemplate doing this until we’ve established a presence on the Moon, Mars, and in the Asteroid Belt.
Second, terraforming any of Jupiter’s moons would involve a considerable amount of time, energy and resources. And given that a lot of these moon’s resources could be harvested for terraforming other worlds (such as Mars and Venus), would it not make sense to terraform these worlds first and circle back to the outer Solar System later?
Third, a terraformed Europa, Ganymede and Callisto would all be water worlds with extremely deep oceans. Would it even be possible to build floating cities on such a world? Or would they be swallowed up by massive tidal waves; or worse, swept off into space by waves so high, they slipped the bonds of the planet’s gravity? And how often would the atmosphere need to be replenished in order to ensure it didn’t get stripped away?
And last, but not least, any act of terraforming these moons would invariably threaten any life that already exists there. And the threat caused by exposure wouldn’t exactly be one-way. Under all of these circumstances, would it not be better to simply establish outposts on the surface, or perhaps within or directly underneath the ice?
All valid questions, and ones which we will no doubt begin to explore once we start mounting research missions to Europa and the other Jovian moons in the future. And depending on what we find there, we might just choose to put down some roots. And in time, we might even begin thinking about renovating the places so more of our kin can drop by. Before we do any of that, we had better make sure we know what we’re doing, and be sure we aren’t doing any harm in the process!
We have written many interesting articles about Jupiter’s Moons here at Universe Today. Here’s What Are Jupiter’s Moons?, Io, Jupiter’s Volcanic Moon, Jupiter’s Moon Europa, Jupiter’s Moon Ganymede, and Jupiter’s Moon Callisto.
To learn more about terraforming, check out The Definitive Guide To Terraforming, How Do We Terraform Mars?, How Do We Terraform Venus?, and How Do We Terraform the Moon? and Could We Terraform Jupiter?
For more information, check out NASA’s Solar System Exploration page on Jupiter’s Moons.
Every year, the NASA Innovative Advanced Concepts (NIAC) program puts out the call to the general public, hoping to find better or entirely new aerospace architectures, systems, or mission ideas. As part of the Space Technology Mission Directorate, this program has been in operation since 1998, serving as a high-level entry point to entrepreneurs, innovators and researchers who want to contribute to human space exploration.
This year, thirteen concepts were chosen for Phase I of the NIAC program, ranging from reprogrammed microorganisms for Mars, a two-dimensional spacecraft that could de-orbit space debris, an analog rover for extreme environments, a robot that turn asteroids into spacecraft, and a next-generation exoplanet hunter. These proposals were awarded $100,000 each for a nine month period to assess the feasibility of their concept.
Of the thirteen proposals, four came from NASA’s own Jet Propulsion Laboratory, with the remainder coming either from other NASA bodies, private research institutions, universities and aerospace companies from around the country. Taken as a whole, these ideas serve to illustrate of the kinds of missions NASA intends to purse in the coming years, as well as the cutting-edge technology they hope to leverage to make them happen.
“The NASA Innovative Advanced Concepts (NIAC) program is one of NASA’s early stage technology development programs. At NIAC, we concentrate on mission studies that demonstrate the benefit of new technologies that are on the very edge of science fiction, but while still remaining firmly rooted in science fact.”
Those proposals that are deemed feasible will be eligible to apply for a Phase II award, which consists of up to $500,000 of additional funding and two more years of concept development. And as with previous years, those concepts that were selected for Phase I were highly representative of NASA’s research and exploration goals, which include missions beyond Low-Earth Orbit (LEO) to near-Earth asteroids, Mars, Venus, and the outer Solar System.
For example, the Jet Propulsion Laboratory’s submissions included a mission that would send a probe back to Venus to explore its atmosphere in greater depth. Known as the Venus Interior Probe Using In-situ Power and Propulsion (VIP-INSPR), this small solar-powered craft would use hydrogen harvested from Venus’ atmosphere – which would be isolated through electrolysis – for altitude control at high altitudes (in a balloon), and as a back-up power source at lower altitudes.
Within Venus’ atmosphere, solar power is no longer a viable option (due to low solar intensity) and primary batteries tend to survive for only an hour or two. What’s more, radioisotope thermoelectric generators (RTGs) – like those that powered the Voyager missions – were dismissed as inefficient for the purposes of a Venus probe.
VIP-INSPR will address these problems by refilling hydrogen on one end of its structure and providing power on the other, thus enabling sustained exploration of the Venusian atmosphere. This is a creative solution to addressing the challenge of keeping a probe powered as it enters Venus’ thick atmosphere, and is sure to have applications beyond the exploration of just Venus.
Similarly, another concept from the JPL involves sending a next-generation rover to Venus, known as the Automaton Rover for Extreme Environments (AREE). This rover seeks to build on the accomplishments of the Soviet Venera and Vega programs, which were the only missions to ever successfully land rovers on Venus’ hostile surface.
Unfortunately, those probes that successfully landed only survived for 23 to 127 minutes before their electronics failed and they could no longer send back information. But by using an entirely mechanical design and a hardened metal structure, the AREE could survive for weeks or months, long enough to collect and return valuable long-term scientific data.
In essence, they proposed reverting back to an ancient concept, using analog gears instead of electronics to enable exploration of the most extreme environment within the Solar System. Beyond Venus, such a probe would also be useful in such hostile environments as Mercury, Jupiter’s radiation belt, and the interior of gas giants, within volcanoes, and perhaps even the mantle of Earth.
Then there is the Icy-moon Cryovolcano Explorer (ICE), another JPL submission which, it is hoped, will one-day explore icy, volcanically-active environments like Europa and Enceladus. The concept of an autonomous underwater vehicle (AUV) is something that has been explored a lot in recent years, but the task of getting such a vehicle to Jupiter or Saturn and beneath the surface of one of their moons presents many challenges.
The ICE team addresses these by designing a surface-to-subsurface robotic system that consists of three modules. The first is the Surface Module (SM), which will remain on the surface after the craft has landed, providing power and communications with Earth. Meanwhile, the Descent Module (DM) will use a combination of roving, climbing, rappelling and hopping to descend into a volcanic vent. Once it reaches the subsurface ocean, it will launch the AUV module, which will explore the subsurface ocean environment and seek out any signs of life.
Last, but not least, the JPL also proposed the Electostatic-Glider (E-Glider) for this year’s NIAC program. This proposal calls for the creation of an active, electrostatically-powered spacecraft to explore airless bodies. Basically, near the surface of comets, asteroids and the Moon, the environment is both airless and full of electrically-charged dust, due to the Sun’s photoelectric bombardment.
A glider equipped with a pair of thin, charged appendages could therefore use the interactions with these particles to create electrostatic lift and propel itself around the body. These appendages are also articulated to direct the levitation force in the whatever direction is most convenient for propulsion and maneuvering. It would also be able to land by simply retracing these appendages (or possibly using thrusters or an anchor).
Beyond NASA, other concepts that made the cut include the Tension Adjustable Novel Deployable Entry Mechanism (TANDEM). In a novel approach, the TANDEM consists of a tensegrity frame with a semi-rigid deployable heat shield composed of 3-D woven carbon-cloth. The same infrastructure is used for every part of the mission, with the shield providing protection during entry, and the frame providing locomotion on the surface.
By reusing the same infrastructure, TANDEM seeks to be the most efficient system ever proposed. The use of tensegrity robotics, which is a largely unexplored concept at present, also provides numerous potential benefits during entry and descent. These include the ability to adjust its shape to achieve an optimal landing, and the ability to reorient itself and charge its aerodynamic center if it gets overturned.
What’s more, conventional tensegrity locomotion depends largely on the actuation of outer cables, which requires mechanical devices in each strut to reel in the cables. However, such a system can prove impractical when used in extreme environments, since it requires that each strut be protected from the environment. This can make the vehicle overly-heavy and contribute to higher launch costs.
The TANDEM, in contrast, relies on only inner cable actuation, which allows the locomotion mechanisms to be housed in the central payload module. Taken together, this means that the TANDEM concept can allow for landings in new locations (opening up the possibility for new missions), can traverse significantly rougher terrain than existing rovers, and provide a higher level of reliability, safety and cost-effectiveness to surface missions.
From the private sector, Made In Space was awarded a Phase I grant for their concept of Reconstituting Asteroids into Mechanical Automata (RAMA). In brief, this concept boils down to using analog computers and mechanisms to convert asteroids into enormous, autonomous mechanical spacecraft, which is likely to have applications when it comes to diverting Potentially-Hazardous Asteroids (PHAs) from Earth, or bringing NEOs closer to Earth to be studied.
The concept was designed with recent developments in additive manufacturing (3-D printing) and in-situ resource utilization (ISRU) in mind. The mission would consist of a series of technically simple robotic components being sent to an asteroid, which would then convert elements of it into very basic parts of spacecraft subsystems – such as guidance, navigation and control (GNC) systems, propulsion, and avionics.
Such a proposal offers cost-saving measures since it eliminates the need to launch all spacecraft subsystems into space. It also offers an affordable and scalable way for NASA to realize future mission concepts, such as the Asteroid Redirect Mission (ARM), the New Frontiers Comet Surface Sample Return, and other Near Earth Object (NEO) applications. If all goes according to plan, Made In Space believes that it will be able to create a space mission that utilizes 3-D printing and ISRU within 20 to 30 years.
Another interesting concept is the Direct Fusion Drive (DFD), which was proposed by Princeton Satellite Systems Inc. Based on the Princeton Field-Reversed Configuration (PFRC) fusion reactor, which is under development at the Princeton Plasma Physics Laboratory, this mission would involve sending a 1000 kg lander to Pluto within 4 to 6 years. By comparison, the New Horizons space probe took roughly 9 years to reach Pluto and didn’t have the necessary fuel to slow down or make a landing.
NASA’s Ames Research Center also proposed a mission that would rely on bioprinting and an end-to-end recycling system to turn Mars’ own atmosphere into replacement electronics. Under the guidance of Dr. Lynn Rothschild, this revolutionary idea calls for small living cells to be printed out in a gel which will then consume resources (like the local atmosphere) and excrete metals, or plastics, or other useful materials.
With this kind of technology, the mass of missions could be significantly reduced, and replacement electronics could be created on-site to address failures or breakdowns. This proposal will not only enhance the likelihood of mission success, but could also have immediate applications to environmental issues here on Earth (not the least of which is the problem of e-waste).
The other winning proposals can be read about here, and include a probe that will analyze the molecular composition of “cold targets” in the Solar System (such as asteroids, comets, planets and moons), a 2-dimensional brane craft that could merge with orbital debris to deorbit it, and the Nano Icy Moons Propellant Harvester (NIMPH) – a proposed Europa mission that would involve Cubesat-sized microlanders harvesting water from the moon’s interior ocean.
There is also the NASA Kennedy Space Center’s Mars Molniya Orbit Atmospheric Resource Mining craft, which would use resources in Mars orbit to make travel to the Red Planet more affordable for future missions. And last, but not least, there was the exoplanet-hunter proposed by Nanohmics Inc., which would use a technique known as stellar echo imaging to provide more detailed imaging of exoplanets than existing techniques.
All in all, this year’s Phase I awards represent a good smattering of the research goals NASA intends to pursue in the coming years. These include, bu are not limited to, studying NEOs, returning to Venus, more missions to Mars and Pluto, and exploring the exotic environments of the outer Solar System. Only time will tell which missions will move from science fiction into the realm of science fact, and which ones will have to be put aside for later consideration.
The post NASA Invests In Radical Game-Changing Concepts For Exploration appeared first on Universe Today.
Be sure to mark your calendar for May 9. On that day, the Solar System’s most elusive planet will pass directly in front of the Sun. The special event, called a transit, happens infrequently. The last Mercury transit occurred more than 10 years ago, so many of us can’t wait for this next. Remember how cool it was to see Venus transit the Sun in 2008 and again in 2012? The views will be similar with one big difference: Mercury’s a lot smaller and farther away than Venus, so you’ll need a telescope. Not a big scope, but something that magnifies at least 30x. Mercury will span just 10 arc seconds, making it only a sixth as big as Venus.
That also means you’ll need a solar filter for your telescope. If you’ve put off buying one, now’s the time to plunk down that credit card. Safe, quality filters are available from many sources including Orion Telescopes, Thousand Oaks Optical, Kendrick Astro Instruments and Amazon.com.
If I might make a suggestion, consider buying a sheet of Baader AstroSolar aluminized polyester film and cutting it to size to make your own filter. Although the film’s crinkly texture might make you think it’s flimsy or of poor optical quality, don’t be deceived by appearances.
The material yields both excellent contrast and a pleasing neutral-colored solar image. You can purchase any of several different-sized films to suit your needs either from Astro-Physics or on Amazon.com. Prices range from $40-90.
Nov. 8, 2006 Transit of Mercury by Dave Kodama
With filter material in hand, just follow these instructions to make your own, snug-fitting telescopic solar filter. Even I can do it, and I kid you not that I’m a total klutz when it comes to building things. If for whatever reason you can’t get a filter, go to Plan B. Put a low power eyepiece in your scope and project an image of the Sun onto a sheet of white paper a foot or two behind the eyepiece.
Since May 9th is a Monday, I’ve a hunch a few of you will be taking the day off. If you can’t, pack a telescope and set it up during lunch hour to share the view with your colleagues. Mercury will spend a leisurely 7 1/2 hours slowly crawling across the Sun’s face, traveling from east to west. The entire transit will be visible across the eastern half of the U.S., most of South America, eastern and central Canada, western Africa and much of western Europe. For the western U.S., Alaska and Hawaii the Sun will rise with the transit already in progress.
|Time Zone||Eastern (EDT)||Central (CDT)||Mountain (MDT)||Pacific (PDT)|
|Transit start||7:12 a.m.||6:12 a.m.||5:12 a.m.||Not visible|
|Mid-transit||10:57 a.m.||9:57 a.m.||8:57 a.m.||7:57 a.m.|
|Transit end||2:42 p.m.||1:42 p.m.||12:42 p.m.||11:42 a.m.|
At first glance, the planet might look like a small sunspot, but if you look closely, you’ll see it’s a small, perfectly circular black dot compared to the out-of-round sunspots which also possess the classic two-part umbra-penumbra structure. Oh yes, it also moves. Slowly to be sure, but much faster than a typical sunspot which takes nearly two weeks to cross the Sun’s face. With a little luck, a few sunspots will be in view during transit time; compared to midnight Mercury their “black” umbral cores will look deep brown.
I want to alert you to four key times to have your eye glued to the telescope; all occur during the 3 minutes and 12 seconds when Mercury enters and exits the Sun. They’re listed below in Universal Time or UT. To convert UT to EDT, subtract 4 hours; CDT 5 hours; MDT 6 hours, PDT 7 hours, AKDT 8 hours and HST 10 hours.
First contact (11:12 UT): Watch for the first hint of Mercury’s globe biting into the Sun just south of the due east point on along the edge of disk’s edge. It’s always a thrill to see an astronomical event forecast years ago happen at precisely the predicted time.
Second contact (11:15 UT): Three minutes and 12 seconds later, the planet’s trailing edge touches the inner limb of the Sun at second contact. Does the planet separate cleanly from the solar limb or briefly remain “connected” by a narrow, black “line”, giving the silhouette a drop-shaped appearance?
This “black drop effect” is caused primarily by diffraction, the bending and interfering of light waves when they pass through the narrow gap between Mercury and the Sun’s edge. You can replicate the effect by bringing your thumb and index finger closer and closer together against a bright backdrop. Immediately before they touch, a black arc will fill the gap between them.
Third contact (18:39 UT): A minute or less before Mercury’s leading edge touches the opposite limb of the Sun at third contact, watch for the black drop effect to return.
Fourth contact (18:42 UT): The moment the last silhouetted speck of Mercury exits the Sun. Don’t forget to mark your calendar for November 11, 2019, date of the next transit, which also favors observers in the Americas and Europe. After that one, the next won’t happen till 2032.
Other interesting visuals to keep an eye out for is a bright ring or aureole that sometimes appears around the planet caused when our brain exaggerates the contrast of an object against a backdrop of a different brightness. Another spurious optical-brain effect keen-eyed observers can watch for is a central bright spot inside Mercury’s black disk. Use high power to get the best views of these obscure but fascinating phenomena seen by many observers during Mercury transits.
While I’ve been talking all “white light” observation, the proliferation of relatively inexpensive and portable hydrogen-alpha telescopes in recent years makes them another viewing option with intriguing possibilities. These instruments show solar phenomena beyond the Sun’s limb, including the flaming prominences normally seen only during a total eclipse. That makes it possible to glimpse Mercury minutes in advance of the transit (or minutes after transit end) silhouetted against a prominence or nudging into the rim furry ring of spicules surrounding the outer limb. Wow!
One final note. Be careful never to look directly at the Sun even for a moment during the transit. Keep your eyes safe! When aiming a telescope, the safest and easiest way to center the Sun in the field of view is to shift the scope up and down and back and forth until the shadow the tube casts on the ground is shortest. Try it.
Good luck and may the weather gods smile on you on May 9!
The post How to Safely Watch Mercury Transit the Sun on May 9 appeared first on Universe Today.
Have you ever seen Mercury? The diminutive innermost world takes the center stage next month, as it transits the Sun as seen from our early perspective on May 9th. This week, we’d like to turn your attention to bashful Mercury’s dusk apparition, which sets up the clockwork celestial gears for this event.
Why is April’s appearance of Mercury special? Well, this elongation is the second of six for 2016, and is the best dusk appearance for Mercury for northern hemisphere observers.
Now, ranking the ‘best’ is a bit of an arcane affair, as not all apparitions of Mercury are created equal. First, Mercury’s orbit is elliptical, meaning it can venture anywhere from 17.9 to 27.8 degrees from the Sun as seen from the Earth. This means you’ll always find Mercury at its best visibility in the dawn or dusk skies. This also means that, while it reaches 50% illumination at greatest elongation—think of Earth, Mercury and the Sun forming a HUGE right triangle in space—its brightness can also vary significantly from one apparition to the next next greatest elongation, from magnitude -0.2 (elongation near perihelion) to +0.7 (elongation near aphelion). And finally, Mercury’s visibility is a matter of observer latitude. April sees the angle of the dusk ecliptic roughly perpendicular to the horizon, thrusting Mercury up out of the mirth for observers based along mid-northern latitudes.
Phew! Got all that? OK, here are some key dates leading up to the May transit:
April 15: Mercury at greatest latitude north of the ecliptic (+7.0 degrees).
April 18: Mercury reaches greatest elongation.
April 28: Mercury 6.8 passes degrees SSW of the Pleiades.
April 29: Mercury stationary; begins retrograde motion.
May 9th: Transit!
Mercury reaches greatest elongation six times in 2016. A great place to explore apparitions of Mercury over time is Formilab’s Mercury Chaser’s Calculator.
Observing and Imaging
Mercury reaches magnitude +0.5, and appears 7” in size on April 15th. Mercury ends the month of April at magnitude +3.7 as a 11” diameter, 8% illuminated crescent. A good way to to find Mercury this week is to imagine it forming a large right triangle with Aldebaran and Capella, both 30 degrees away.
At the telescope, Mercury will show a tiny half to crescent phase, mimicking the Moon. The heavy airmass low to the horizon will cause Mercury to shimmer and dance, making seeing cruddy (a technical term!) and picking out surface detail next to impossible. We knew little about Mercury right up until the Space Age. As a child of the 1970s, I remember how you could still find astronomy books quoting a wild range of rotation periods.
Exploring Mercury, Near and Far
Today, we know Mercury spins on its axis once every 58.6 Earth days. This is a 2:3 resonance with the Mercurial ‘year,’ and from certain locales on the surface, you would actually see the Sun rise, reverse direction, and set again! Mercury also resembles our own Moon, minus the maria.
To date, only NASA has visited Mercury, first during the three Mariner 10 flybys in 1974 and 1975, and with Mercury MESSENGER, which became the only human-built spacecraft to orbit around Mercury after three flybys starting on March 18th, 2011. Messenger also holds the distinction of being the only human artifact to touch Mercury, crashing into the planet on April 30th, 2015.
The European Space Agency will carry on the legacy of Mercury exploration, with the launch of its BepiColombo spacecraft in January of next year. BepiColombo will enter orbit around Mercury on New Year’s Day, 2024.
And the orbit of Mercury played a key role in 20th century science. Namely, the anomalous precession of its perihelion could not be explained away by Newtonian mechanics. This led to the prediction of a world dubbed Vulcan on an orbit interior to Mercury’s own. Spurious sightings of Vulcan persisted, and the world even made the list of solar system planets through the end of the 19th century… but it took Einstein’s theory of general relativity to do away with the need for Vulcan and explain the persistent advance of Mercury’s orbit.
Follow that fleeting world, as Mercury will transit the face of the Sun as seen from the Earth on May 9th. This is one of only 14 transits of Mercury for the 21st century. The last occurred on November 8th, 2006, and the next is on November 11th, 2019. We remember courting heat stroke during the 2006 transit, as we supported public viewing from the lawn surrounding the Flandrau observatory on the Tucson, Arizona campus. Mercury enters the field of view of the Solar Heliospheric Observatory’s (SOHO) LASCO C3 camera on May 4th leading up to the transit, and exits on May 14th, headed once again back in to the dawn sky.
Bob King will have more out on the transit of Mercury for Universe Today very soon… watch this space!
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