A concentrated three-day search for a mysterious, unseen planet in the far reaches of our own solar system has yielded four possible candidates. The search for the so-called Planet 9 was part of a real-time search with a Zooniverse citizen science project, in coordination with the BBC’s Stargazing Live broadcast from the Australian National University’s […]
Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet in the outer reaches of our Solar System — likely located out past Pluto — and since then, the search has been on. The latest research continues to show signs of an unseen planet, the hypothetical […]
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Host: Fraser Cain (@fcain) Guests: Carolyn Collins Petersen (thespacewriter.com / space.about.com / @spacewriter ) Paul M. Sutter (pmsutter.com / @PaulMattSutter) Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier ) Their stories this week: New studies of Boyajian’s Star Breakthrough Starshot hunting for planets Probing the Nearby Space Between Stars Looking for the stuff of life A new […]
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Pluto can’t seem to catch a break lately. After being reclassified in 2006 by the International Astronomical Union, it seemed that what had been the 9th planet of the Solar System was now relegated to the status of “dwarf planet” with the likes of Ceres, Eris, Haumea, and Makemake. Then came the recent announcements that the title of “Planet 9” may belong to an object ten times the mass of Earth located 700 AU from our Sun.
And now, new research has been produced that indicates that Pluto may need to be reclassified again. Using data provided by the New Horizons mission, researchers have shown that Pluto’s interaction with the Sun’s solar wind is unlike anything observed in the Solar System thus far. As a result, it would seem that the debate over how to classify Pluto, and indeed all astronomical bodies, is not yet over.
In a study that appeared in the Journal of Geophysical Research, a team of researchers from the Southwest Research Institute – with support from the Johns Hopkins University Applied Physics Laboratory, the Laboratory of Atmospheric and Space Physics at University of Colorado and other institutions – examined data obtained by the New Horizon mission’s Solar Wind Around Pluto (SWAP) instrument.
Basically, solar wind effects every body in the Solar System. Consisting of electrons, hydrogen ions and alpha particles, this stream of plasma flows from our Sun to the edge of the Solar System at speeds of up to 160 million kilometers per hour. When it comes into contact with a comet, there is a discernible region behind the comet where the wind speed slows discernibly.
Meanwhile, where solar wind encounters a planet, the result is an abrupt diversion in its path. The region where this occurs around a planet is known as a “bow shock”, owing to the distinctive shape it forms. The very reason the New Horizons mission was equipped with the SWAP instrument was so that it could gather solar wind data from the edge of the Solar System and allow astronomers to create more accurate models of the environment.
But when the Southwestern Research Institute team examined the SWAP data, which was obtained during the New Horizons’ July 2015 flyby of Pluto, what they found was surprising. Previously, most researchers thought that Pluto was characterized more like a comet, which has a large region of gentle slowing of the solar wind, as opposed to the abrupt diversion solar wind encounters at a planet like Mars or Venus.
What they found instead was that the dwarf planet’s interaction with solar wind was something the fell between that of a comet and a planet. As Dr. David J. McComas – the Assistant Vice President of the Space Science and Engineering Division at the Southwest Research Institute – said during a NASA news release about the study: “This is a type of interaction we’ve never seen before anywhere in our solar system. The results are astonishing.”
Examining both the lighter hydrogen ions that are thrown off by the Sun, and the heavier methane ions that are produced by Pluto, they found that the former showed a 20% rate of deceleration behind Pluto. This, and the bow shock Pluto produces, were both consistent with that of a comet. At the same time, they found that Pluto’s gravity was strong enough that it is able to retain the heavier methane ions, which is consistent with a planet.
Between these two readings, it seems that Pluto is something of an anomaly, behaving as something of a hybrid. Yet another surprise from a celestial body that has been full of them lately. And under the circumstances, it may lead to another round of “classification debates”, as astronomers attempt to find a new class for bodies that behave like both comets and planets.
As Alan Stern of the Southwestern Research Institute, and the principal investigator of the New Horizon’s mission, explained, “These results speak to the power of exploration. Once again we’ve gone to a new kind of place and found ourselves discovering entirely new kinds of expressions in nature.”
Further Reading: Journal of Geophysical Research
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Three more potentially Earthlike worlds have been discovered in our galactic backyard, announced online today by the European Southern Observatory. Researchers using the 60cm TRAPPIST telescope at ESO’s La Silla observatory in Chile have identified three Earth-sized exoplanets orbiting a star just 40 light-years away.
The star, originally classified as 2MASS J23062928-0502285 but now known as TRAPPIST-1, is an dim “ultracool” brown dwarf only .05% as bright as our Sun . Located in the constellation Aquarius, it’s now the 37th-farthest star known to host orbiting exoplanets.
The exoplanets were discovered via the transit method (TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope) through which the light from a star is observed to dim slightly by planets passing in front of it from our point of view.
As a brown dwarf “failed star” TRAPPIST-1 is a very small and dim and isn’t easily visible from Earth, but it’s its very dimness that has allowed its planets to be discovered with existing technology. Their subtle silhouettes may have been lost in the glare of larger, brighter stars.
Follow-up measurements of the three exoplanets indicated that they are all approximately Earth-sized and have temperatures ranging from Earthlike to Venuslike (which is, admittedly, a fairly large range.) They orbit their host star very closely with periods measured in Earth days, not years.
“With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun,” said Michael Gillon, lead author of the research paper. “The structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”
Although these three new exoplanets are Earth-sized they do not yet classify as “potentially habitable,” at least by the standards of the Planetary Habitability Laboratory (PHL) operated by the University of Puerto Rico at Arecibo. The planets fall outside PHL’s required habitable zone; two are too close to the host star and one is too far away.
This does not mean that the exoplanets are completely uninhabitable, though; it’s entirely possible that there are regions on or within them where life could exist, not unlike Mars or some of the moons in our own Solar System.
Discovering three planets orbiting such a small yet extremely common type of star hints that there are likely many, many more such worlds in our galaxy and the Universe as a whole.
“So far, the existence of such ‘red worlds’ orbiting ultra-cool dwarf stars was purely theoretical, but now we have not just one lonely planet around such a faint red star but a complete system of three planets,” said study co-author Emmanuel Jehin.
The team’s research was presented in a paper entitled “Temperate Earth-sized planets transiting a nearby ultracool dwarf star” and will be published in Nature.
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All the worlds may be ours except Europa but that only makes the ice-covered moon of Jupiter all the more intriguing. Beneath Europa’s thin crust of ice lies a tantalizing global ocean of liquid water somewhere in the neighborhood of 100 kilometers deep—which adds up to more liquid water than is on the entire surface of the Earth. Liquid water plus a heat source(s) to keep it liquid plus the organic compounds necessary for life and…well, you know where the thought process naturally goes from there.
And now it turns out Europa may have even more of a heat source than we thought. Yes, a big component of Europa’s water-liquefying warmth comes from tidal stresses enacted by the massive gravity of Jupiter as well as from the other large Galilean moons. But exactly how much heat is created within the moon’s icy crust as it flexes has so far only been loosely estimated. Now, researchers from Brown University in Providence, RI and Columbia University in New York City have modeled how friction creates heat within ice under stress, and the results were surprising.
Although 3,100-km-wide Europa is coated in ice and technically has the smoothest surface in the Solar System, it’s far from featureless. Its frozen crust features enormous regions of broken “chaos terrain” and is covered in long, crisscrossing fractures filled with reddish-brown material (which may be a form of sea salt), as well as crumpled, mountain-like ridges that appear curiously fresh.
These ridges are thought to be a result of a form of tectonics, except not with plates of rock like on Earth but rather shifting slabs of frozen water. But where the energy needed to drive that process is coming from—and what happens to all the frictional heat created during it—isn’t well known.
“People have been using simple mechanical models to describe the ice,” said geophysicist Christine McCarthy, Lamont Assistant Research Professor at Columbia University who led the research while a graduate student at Brown University. “They weren’t getting the kinds of heat fluxes that would create these tectonics. So we ran some experiments to try to understand this process better.”
By mechanically subjecting ice samples to various forms of pressure and stress, similar to the conditions that would be found on Europa as it orbits Jupiter, the researchers found that most of the heat is generated within deformities in the ice, rather than between the individual grains as was previously thought. This difference means there’s likely a lot more heat moving through Europa’s ice layers, which would affect both its behavior and its thickness.
“Those physics are first order in understanding the thickness of Europa’s shell,” said Reid Cooper, Earth science professor and McCarthy’s research partner at Brown. “In turn, the thickness of the shell relative to the bulk chemistry of the moon is important in understanding the chemistry of that ocean. And if you’re looking for life, then the chemistry of the ocean is a big deal.”
When it comes to Europa’s icy crust there have traditionally been two camps of thought: the thin-icers and the thick-icers. Thin-icers estimate the moon’s crust to be at most only a few kilometers thick—possibly coming very close to the surface in places, if not breaking through entirely—while those in the thick-ice camp think it could be tens of times thicker. While there are data to support both hypotheses, it remains to be seen which these new findings will best support.
Luckily we won’t have to wait terribly long to find out how thick the moon’s icy crust really is. A recently-approved NASA mission will launch to Europa in the 2020s to explore its surface, interior composition, and potential habitability. The mission may (i.e., should) also include a lander, although of what fashion has yet to be determined. But when the data from that mission do finally come in, many of our long-standing questions about this mystifying icy world will finally be answered.
The team’s research is published in the June 1 issue of Earth and Planetary Science Letters.
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The Solar System is a spinny place. Everything’s turning turning. But if you look closely, there are some pretty strange spins going on. Today we talk about how everything started turning, and the factors that still “impact” them today. Visit the Astronomy Cast Page to subscribe to the audio podcast! We record Astronomy Cast as […]
TW Hydrae is a special star. Located 175 light years from Earth in the constellation Hydra the Water Snake, it sits at the center of a dense disk of gas and dust that astronomers think resembles our solar system when it was just 10 million years old. The disk is incredibly clear in images made using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which employs 66 radio telescopes sensitive to light just beyond that of infrared. Spread across more than 9 miles (15 kilometers), the ALMA array acts as a gigantic single telescope that can make images 10 times sharper than even the Hubble Space Telescope.
Astronomers everywhere point their telescopes at TW Hydrae because it’s the closest infant star in the sky. With an age of between 5 and 10 million years, it’s not even running on hydrogen fusion yet, the process by which stars convert hydrogen into helium to produce energy. TW Hydrae shines from the energy released as it contracts through gravity. Fusion and official stardom won’t begin until it’s dense enough and hot enough for fusion to fire up in its belly.
We see most protoplanetary disks at various angles, but TW’s has a face-on orientation as seen from Earth, giving astronomers a rare, undistorted view of the complete disk around the star. The new images show amazing detail, revealing a series of concentric bright rings of dust separated by dark gaps. There’s even indications that a planet with an Earth-like orbit has begun clearing an orbit.
“Previous studies with optical and radio telescopes confirm that TW Hydrae hosts a prominent disk with features that strongly suggest planets are beginning to coalesce,” said Sean Andrews with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA and lead author on a paper published today in the Astrophysical Journal Letters.
Pronounced gaps that show up in the photos above are located at 1.9 and 3.7 billion miles (3-6 billion kilometers) from the central star, similar to the average distances from the sun to Uranus and Pluto in the solar system. They too are likely to be the results of particles that came together to form planets, which then swept their orbits clear of dust and gas to sculpt the remaining material into well-defined bands. ALMA picks up the faint emission of submillimeter light emitted by dust grains in the disk, revealing details as small as 93 million miles (150 million kilometers) or the distance of Earth from the sun
“This is the highest spatial resolution image ever of a protoplanetary disk from ALMA, and that won’t be easily beaten in the future!” said Andrews.
Earlier ALMA observations of another system, HL Tauri, show that even younger protoplanetary disks — a mere 1 million years old — look remarkably similar. By studying the older TW Hydrae disk, astronomers hope to better understand the evolution of our own planet and the prospects for similar systems throughout the Milky Way.
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