Bye, Bye Rosetta — We’ll Miss You!

Copyright: ESA with changes to annotations by the author

Rosetta awoke from a decade of deep-space hibernation in January 2014 and immediately got to work photographing, measuring and sampling comet 67P/C-G. On September 30 it will sleep again but this time for eternity. Mission controllers will direct the probe to impact the comet’s dusty-icy nucleus within 20 minutes of 10:40 Greenwich Time (6:40 a.m. EDT) that Friday morning. The high-resolution OSIRIS camera will be snapping pictures on the way down, but once impact occurs, it’s game over, lights out. Rosetta will power down and go silent.

Nearly three years have passed since Rosetta opened its eyes on 67P, this curious, bi-lobed rubber duck of a comet just 2.5 miles (4 km) across with landscapes ranging from dust dunes to craggy peaks to enigmatic ‘goosebumps’. The mission was the first to orbit a comet and dispatch a probe, Philae, to its surface. I think it’s safe to say we learned more about what makes comets tick during Rosetta’s sojourn than in any previous mission.

So why end it? One of the big reasons is power. As Rosetta races farther and farther from the Sun, less sunlight falls on its pair of 16-meter-long solar arrays. At mid-month, the probe was over 348 million miles (560 million km) from the Sun and 433 million miles (697 million km) from Earth or nearly as far as Jupiter. With Sun-to-Rosetta mileage increasing nearly 620,000 miles (1 million km) a day, weakening sunlight can’t provide the power needed to keep the instruments running.
Rosetta’s last orbits around the comet

Rosetta’s also showing signs of age after having been in the harsh environment of interplanetary space for more than 12 years, two of them next door to a dust-spitting comet. Both factors contributed to the decision to end the mission rather than put the probe back into an even longer hibernation until the comet’s next perihelion many years away.

Since August 9, Rosetta has been swinging past the comet in a series of ever-tightening loops, providing excellent opportunities for close-up science observations. On September 5, Rosetta swooped within 1.2 miles (1.9 km) of 67P/C-G’s surface. It was hoped the spacecraft would descend as low as a kilometer during one of the later orbits as scientists worked to glean as much as possible before the show ends.

The final of 15 close flyovers will be completed today (Sept. 24) after which Rosetta will be maneuvered from its current elliptical orbit onto a trajectory that will eventually take it down to the comet’s surface on Sept. 30.

The beginning of the end unfolds on the evening of the 29th when Rosetta spends 14 hours free-falling slowly towards the comet from an altitude of 12.4 miles (20 km) — about 4 miles higher than a typical commercial jet — all the while collecting measurements and photos that will be returned to Earth before impact. The last eye-popping images will be taken from a distance of just tens to a hundred meters away.

The landing will be a soft one, with the spacecraft touching down at walking speed. Like Philae before it, it will probably bounce around before settling into place. Mission control expects parts of the probe to break upon impact.

Taking into account the additional 40 minute signal travel time between Rosetta and Earth on the 30th, confirmation of impact is expected at ESA’s mission control in Darmstadt, Germany, within 20 minutes of 11:20 GMT (7:20 a.m. EDT). The times will be updated as the trajectory is refined. You can watch live coverage of Rosetta’s final hours on ESA TV .
ESAHangout: Preparing for Rosetta’s grand finale

“It’s hard to believe that Rosetta’s incredible 12.5 year odyssey is almost over, and we’re planning the final set of science operations, but we are certainly looking forward to focusing on analyzing the reams of data for many decades to come,” said Matt Taylor, ESA’s Rosetta project scientist.

Plans call for the spacecraft to impact the comet somewhere within an ellipse about 1,300 x 2,000 feet (600 x 400 meters) long on 67P’s smaller lobe in the region known as Ma’at. It’s home to several active pits more than 328 feet (100 meters) in diameter and 160-200 feet (50-60 meters) deep, where a number of the comet’s dust jets originate. The walls of the pits are lined with fascinating meter-sized lumpy structures called ‘goosebumps’, which scientists believe could be early ‘cometesimals’, the icy snowballs that stuck together to create the comet in the early days of our Solar System’s formation.

During free-fall, the spacecraft will target a point adjacent to a 425-foot (130 m) wide, well-defined pit that the mission team has informally named Deir el-Medina, after a structure with a similar appearance in an ancient Egyptian town of the same name. High resolution images should give us a spectacular view of these enigmatic bumps.

While we hate to see Rosetta’s mission end, it’s been a blast going for a 2-year-plus comet ride-along.

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Spotlight On Pluto’s Frozen Polar Canyons

This enhanced color view Long canyons run vertically across the polar area—part of the informally named Lowell Regio, named for Percival Lowell, who founded Lowell Observatory and initiated the search that led to Pluto’s discovery. The widest of the canyons is about 45 miles (75 kilometers) wide and runs close to the north pole. Roughly parallel subsidiary canyons to the east and west are approximately 6 miles (10 kilometers) wide.

Pluto’s frozen nitrogen custard “heart” has certainly received its share of attention. Dozens of wide and close-up photos homing on this fascinating region rimmed by mountains and badlands have been relayed back to Earth by NASA’s New Horizons probe after last July’s flyby. For being only 1,473 miles (2,370 km) in diameter, Pluto displays an incredible diversity of landscapes.

This week, the New Horizons team shifted its focus northward, re-releasing an enhanced color image of the north polar area that was originally part of a high-resolution full-disk photograph of Pluto. Inside of the widest canyon, you can trace the sinuous outline of a narrower valley similar in outward appearance to the Moon’s Alpine Valleycut by a narrow, curvy rill that once served as a conduit for lava.

We see multiple canyons in Pluto’s polar region, their walls broken and degraded compared to canyons seen elsewhere on the planet. Signs that they may be older and made of weaker materials and likely formed in ancient times when Pluto was more tectonically active. Perhaps they’re related to that long-ago dance between Pluto and its largest moon Charon as the two transitioned into their current tidally-locked embrace.

In the lower right corner of the image, check out those funky-shaped pits that resemble the melting outlines of boot prints in the snow. They reach 45 miles (70 km) across and 2.5 miles (4 km) deep and may indicate locations where subsurface ice has melted or sublimated (vaporized) from below, causing the ground to collapse.

Notice the variation in color across the landscape from yellow-orange to pale blue. High elevations show up in a distinctive yellow, not seen elsewhere on Pluto, with lower elevations and latitudes a bluish gray. New Horizons’ infrared measurements show abundant methane ice across the Lowell Region, with relatively little nitrogen ice. The yellow terrains may be older methane deposits that have been more processed by solar UV light than the bluer terrain. The color variations are especially striking in the area of the collapse pits.

Pluto’s icy riches include not only methane and nitrogen but also water, which forms the planet’s bedrock. NASA poetically refers to the water ice as “the canvas on which (Pluto’s) more volatile ices paint their seasonally changing patterns”. Recent images made in infrared light shows little or no water ice in the informally named places called Sputnik Planum (the left or western region of Pluto’s “heart”) and Lowell Regio. This indicates that at least in these regions, Pluto’s bedrock remains well hidden beneath a thick blanket of other ices such as methane, nitrogen and carbon monoxide.

To delve more deeply into Pluto, visit the NASA’s photojournal archive, where you’ll find 130 photos (and counting!) of the dwarf planet and its satellites.

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