Rosetta fell silent moments after 6:19 a.m. Eastern Time (12:19 UT) this morning, when it gently crashed into 67P/C-G 446 million miles (718 million km) from Earth. As the probe descended to the comet’s bouldery surface of the comet in free fall, it snapped a series of ever-more-detailed photographs while gathering the last bits data on the density and composition of cometary gases, surface temperature and gravity field before the final curtain was drawn.
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.
Dr. Frank Timmes is an astrophysicist at Arizona State University and will be discussing online astronomy education and the Global Freshman Academy. His interests include the universe’s evolving composition and its implications for life in the universe. Dr. Timmes’ current area of research is nuclear astrophysics and the creation of the periodic table.
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The search is over, and looking at these images, no wonder it was so hard to find the little Philae lander!
The high-resolution camera on board the Rosetta spacecraft has finally spotted Philae “wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko,” the ESA team said. They also said that now, seeing the lander’s orientation, it’s clear why establishing communications was so difficult following its landing on November 12, 2014.
Rosetta, orbiting the comet and getting ready for its own demise/touchdown on 67P, focused its OSIRIS narrow-angle camera towards a few candidate sites on September 2, 2016 as the orbiter came just 2.7 km of the comet’s surface. Clearly visible in the zoomed in versions are the main body of the lander, along with two of its three legs.
“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” says Cecilia Tubiana of the OSIRIS camera team, the first person to see the images when they were downlinked from Rosetta on September 4.
Tubiana told Universe Today via email that Philae wasn’t too hard to find in the images. “Philae was in hiding in shadow, and as soon as we stretched the brightness to ‘see’ into the shadow, Philae was there!”
She added that nothing else about Philae’s condition has been revealed from the images so far.
The Philae lander was last seen after it first touched down at a region called Agilkia on the odd-shaped, two-lobed comet 67P. During its dramatic touchdown, the lander flew, landed, bounced and then repeated that process for more than two hours across the surface, with three or maybe four touchdowns. The harpoons that were to anchor Philae to the surface failed to fire, and scientists estimated the lander may have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in the shadows of a cliff on the comet. After three days, Philae’s primary battery ran out of power and the lander went into hibernation, only to wake up again and communicate briefly with Rosetta in June and July 2015 as the comet came closer to the Sun and more power was available.
Philae’s final location had been plotted but until yesterday, never actually seen by Rosetta’s cameras. Radio ranging data was used to narrow down the search to an area spanning a few tens of meters, and a number of potential candidate objects were identified in relatively low-resolution images taken from larger distances.
Compare some of the features of the cliff in the image above to this image taken by Philae of its surroundings:
“After months of work, with the focus and the evidence pointing more and more to this lander candidate, I’m very excited and thrilled that we finally have this all-important picture of Philae sitting in Abydos,” said ESA’s Laurence O’Rourke, who has been coordinating the search efforts over the last months at ESA, with the OSIRIS and SONC/CNES teams.
At 2.7 km, the resolution of the OSIRIS narrow-angle camera is about 5 cm/pixel, which is sufficient to reveal features of Philae’s 1 m-sized body and its legs.
“This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” says Matt Taylor, ESA’s Rosetta project scientist.
The discovery comes less than a month before Rosetta descends to the comet’s surface. On September 30, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in a region called Ma’at, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure.
“Now that the lander search is finished we feel ready for Rosetta’s landing, and look forward to capturing even closer images of Rosetta’s touchdown site,” adds Holger Sierks, principal investigator of the OSIRIS camera.
The Rosetta team said they would be providing more details about the search as well as more images in the near future.
ESA’s Philae lander, the first spacecraft to successfully soft-land on the surface of a comet and former piggyback partner to Rosetta, has not been in communication since July of 2015 and, with 67P now six months past perihelion and heading deeper out into the Solar System, it’s not likely it will ever be heard from again.
How would you like to see one of the most famous comets with your own eyes? Comet 67P/Churyumov-Gerasimenko plies the morning sky, a little blot of fuzzy light toting an amazing visitor along for the ride — the Rosetta spacecraft. When you look at the coma and realize a human-made machine is buzzing around inside, it seems unbelievable.
If you have a 10-inch or larger telescope, or you’re an experienced amateur with an 8-inch and pristine skies, 67P is within your grasp. The comet glows right around magnitude +12, about as bright as it will get this apparition. Periodic comets generally appear brightest around and shortly after perihelion or closest approach to the Sun, which for 67P/C-G occurred back on August 13.
You’ll be looking for a small, 1-arc-minute-diameter, compact, circular patch of nebulous light shortly before dawn when it’s highest in the east. Rosetta’s Comet will spend the remainder of August slicing across Gemini the Twins north of an nearly parallel to the ecliptic. I spotted 67P/C-G for the first time this go-round about a week ago in my 15-inch (37 cm) reflector. While it appears like a typical faint comet, thanks to Rosetta, we know this particular rough and tumble mountain of ice better than any previous comet. Photographs show rugged cliffs, numerous cracks due to the expansion and contraction of ice, blowholes that serve as sources for jets and smooth plains blanketed in fallen dust.
The jets are geyser-like sprays of dust and gas that loft grit and rocks from the comet’s interior and surface into space to create a coma or temporary atmosphere. This is what you’ll see in your telescope. And if you’re patient, you’ll even be able to catch this glowing tadpole on the move. I was surprised at its speed. After just 20 minutes, thanks to numerous field stars that acted as references, I could easily spot the comet’s eastward movement using a magnification of 245x.
Tomorrow morning, 67P/C-G passes very close to the magnitude +5 star Omega Geminorum. While this will make it easy to locate, the glare may swamp the comet. Set your alarm for an hour before dawn’s start to allow time to set up a telescope, dark-adapt your eyes and track down the field where the comet will be that morning using low magnification.
Once you’ve centered 67P/C-G’s position, increase the power to around 100x-150x and use averted vision to look for a soft, fuzzy patch of light. If you see nothing, take it to the next level (around 200-250x) and carefully search the area. The higher the magnification, the darker the field of view and easier it will be to spot it.
Besides being relatively faint, the comet doesn’t get very high in the east before the onset of twilight. Low altitude means the atmosphere absorbs a share of the comet’s light, making it appear even fainter. Not that I want to dissuade you from looking! There’s nothing like seeing real 67P photons not to mention the adventure and sense of accomplishment that come from finding the object on your own.
As we advance into late summer and early fall, 67P/C-G will appear higher up but also be fading. Now through about August 27 and again from September 10-24 will be your best viewing times. That’s when the Moon’s absent from the sky.
Given the comet’s current distance from Earth of 165 million miles and apparent visual size of just shy of 1 arc minute, the coma measures very approximately 30,000 miles across. Rosetta orbits the comet’s 2.5-mile-long icy nucleus at a distance of about 115 miles (186 km), meaning it’s snug up against the nuclear center from our point of view on the ground.
The idea of panspermia — that life on Earth originated from comets or asteroids bombarding our planet — is not new. But new research may have given the theory a boost. Scientists from Japan say their experiments show that early comet impacts could have caused amino acids to change into peptides, becoming the first building blocks of life. Not only would this help explain the genesis of life on Earth, but it could also have implications for life on other worlds.
Dr. Haruna Sugahara, from the Japan Agency for Marine-Earth Science and Technology in Yokahama, and Dr. Koichi Mimura, from Nagoya University said they conducted “shock experiments on frozen mixtures of amino acid, water ice and silicate (forsterite) at cryogenic condition (77 K),” according to their paper. “In the experiments, the frozen amino acid mixture was sealed into a capsule … a vertical propellant gun was used to [simulate] impact shock.”
They analyzed the post-impact mixture with gas chromatography, and found that some of the amino acids had joined into short peptides of up to 3 units long (tripeptides).
Based on the experimental data, the researchers were able to estimate that the amount of peptides produced would be around the same as had been thought to be produced by normal terrestrial processes (such as lighting storms or hydration and dehydration cycles).
“This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth,” said Sugahara. “It also opens the likelihood that we will have seen similar chemical evolution in other extraterrestrial bodies, starting with cometary-derived peptides.”
The earliest known fossils on Earth are from about 3.5 billion years ago and there is evidence that biological activity took place even earlier. But there’s evidence that early Earth had little water and carbon-based molecules on the Earth’s surface, so how could these building blocks of life delivered to the Earth’s surface so quickly? This was also about the time of the Late Heavy Bombardment, and so the obvious answer could be the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules.
Space missions to comets are helping to confirm this possibility. The 2004 Stardust mission found the amino acid when it collected particles from Comet Wild 2. When NASA’s Deep Impact spacecraft crashed into Comet Tempel 1 in 2005, it discovered a mixture of organic and clay particles inside the comet. One theory about the origins of life is that clay particles act as a catalyst, allowing simple organic molecules to get arranged into more and more complex structures.
The news from the current Rosetta mission to comet 67P/Churyumov-Gerasimenko also indicates that comets are a rich source of materials, and more discoveries are likely to be forthcoming from that mission.
“Two key parts to this story are how complex molecules are initially generated on comets and then how they survive/evolve when the comet hits a planet like the Earth,” said Professor Mark Burchell from the University of Kent in the UK, commenting on the new research from Japan. “Both of these steps can involve shocks which deliver energy to the icy body… building on earlier work, Dr. Sugahara and Dr. Mimura have shown how amino acids on icy bodies can be turned into short peptide sequences, another key step along the path to life.”
“Comet impacts are normally associated with mass extinction on Earth, but this works shows that they probably helped kick-start the whole process of life in the first place,” said Sugahara. “The production of short peptides is the key step in the chemical evolution of complex molecules. Once the process is kick-started, then much less energy is needed to make longer chain peptides in a terrestrial, aquatic environment.”
The scientists also indicated that similar “kickstarting” could have happened in other places in our Solar System, such as on the icy moons Europa and Enceladus, as they likely underwent a similar comet bombardment.
Sequence of OSIRIS narrow-angle camera images from 12 August 2015, just a few hours before the comet reached perihelion. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
See hi res images below[/caption]
A spectacular display of celestial fireworks like none ever witnessed before, burst forth from Rosetta’s comet right on time – commemorating the Europeans spacecraft’s history making perihelion passage after a year long wait of mounting excitement and breathtaking science.
And the perihelion passage did not disappoint – living up to its advance billing by spewing forth an unmatched display of otherworldly outbursts of gas jets and dust particles due to surface heating from the warming effects of the sun as the comet edged ever closer, coming within 186 million kilometers of mighty Sol.
ESA has released a brand new series of images, shown above and below, documenting sparks flying – as seen by Rosetta’s OSIRIS narrow-angle camera and NAVCAM wider angle cameras on August 12 and 13 – just a few hours before the rubby ducky shaped comet reached perihelion along its 6.5-year orbit around the sun.
Indeed the navcam camera image below was taken just an hour before the moment of perihelion, at 01:04 GMT, from a distance of around 327 kilometers!
Frozen ices are seen blasting away from the comet in a hail of gas and dust particles as rising solar radiation heats the nucleus and fortifies the comet’s atmosphere, or coma, and its tail.
After a decade long chase of over 6.4 billion kilometers (4 Billion miles), ESA’s Rosetta spacecraft arrived at the pockmarked Comet 67P/Churyumov-Gerasimenko exactly a year ago on Aug. 6, 2014 for history’s first ever attempt to orbit a comet for long term study.
In the interim, Rosetta also deployed the piggybacked Philae lander for history’s first landing on a comet on Nov. 12, 2014.
In fact, measurements from Rosetta’s science instruments confirm the comet is belching a thousand times more water vapor today than was observed during Rosetta’s arrival a year ago. It’s spewing some 300 kg of water vapour every second now, compared to just 300 g per second upon arrival. That equates to two bathtubs per second now in Aug. 2015 vs. two small glasses of water per second in Aug. 2014.
Besides gas, 1000 kg of dust per second is simultaneously erupting from the nucleus, “creating dangerous working conditions for Rosetta,” says ESA.
“In recent days, we have been forced to move even further away from the comet. We’re currently at a distance of between 325 km and 340 km this week, in a region where Rosetta’s startrackers can operate without being confused by excessive dust levels – without them working properly, Rosetta can’t position itself in space,” comments Sylvain Lodiot, ESA’s spacecraft operations manager, in an ESA statement.
Here’s an OSIRIS image taken just hours prior to perihelion, that’s included in the lead animation of this story.
The period of the comet’s peak intensity, as seen in all these images, is expected to continue past perihelion for several weeks at least and fulfils the dreams of a scientific goldmine for all the research teams and hundreds of researchers involved with Rosetta and Philae.
“Activity will remain high like this for many weeks, and we’re certainly looking forward to seeing how many more jets and outburst events we catch in the act, as we have already witnessed in the last few weeks,” says Nicolas Altobelli, acting Rosetta project scientist.
And Rosetta still has lots of fuel, and just as important – funding – to plus up its ground breaking science discoveries.
ESA recently granted Rosetta a 9 month mission extension to continue its research activities as well as having been given the chance to accomplish one final and daring historic challenge.
Engineers will attempt to boldly go and land the probe on the undulating surface of the comet.
Officials with the European Space Agency (ESA) gave the “GO” on June 23 saying “The adventure continues” for Rosetta to march forward with mission operations until the end of September 2016.
If all continues to go well “the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko” said ESA.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Why is landing on a comet so difficult and what does this tell us about future missions to comets and asteroids?
Us nerds were riveted by the coverage of the ESA’s Rosetta mission and its arrival at Comet 67/P in 2014. One such nerd is Paco Juarez, friend of the show and patron. He wanted to know why is it so darned hard to land on a comet?
In 2014, the tiny Philae Lander detached from the spacecraft and slowly descended down to the surface of the comet. If everything went well, it would have gracefully touched down and then sent back a pile of information about this filthy roving snowball.
As you know, the landing didn’t go according to plan. Instead of gently touching down on 67/P, Philae bounced off the surface of the comet like a tennis ball dropped from a tower, and rose a kilometer off the surface. Then more descending, and more bouncing, finally settling down on rugged terrain, surrounded by crevices and large boulders. At that point, engineers lost contact with the lander, and so much science went undone.
If I recorded this video a few months ago, that would have been the end of the story. You know how this goes, space exploration is hard and dangerous, don’t be surprised when your missions fail and space unfeelingly smashes up your pretty little robot probes with their little gold foil 27 pieces of flair.
Fortunately, I’m able to report that ESA regained contact with the Philae lander on June 13, 2015, resuming its mission, and scientific operations.
But why is landing on a comet so difficult and what does this tell us about future robotic and human missions to smaller comets and asteroids? When ESA engineers designed Philae, they knew it was going to be very difficult to land on a comet like 67/P because they have a such a low gravity. And they have low gravity because they’re little.
On Earth, 6 septillion tonnes of rock and metal give you an escape velocity of 11.2 km/s. That’s how fast you need to be able to jump in order to leave the planet entirely. But the escape velocity of 67/P is only 1 m/s. You could trip off the comet and never return. Whilst small children threw rocks at you from the surface as you drifted away.
Philae was built with harpoon drills in its landing struts. The moment the lander touched the surface of the comet, those harpoons were supposed to fire, securing the lander. The surface of the comet was softer than scientists had anticipated, and the harpoons didn’t fire. Or possibly they were broken and couldn’t fire. Space is hard. Whatever the case, without being able to grab onto the surface, it used the comet as a bouncy castle.
We’re learning what it takes to land on lower mass objects like comets and asteroids. NASA’s OSIRIS-REx mission will visit Comet Bennu, and send a lander down to the surface of the asteroid. From there it’ll pick up a few samples, and return them back to Earth. It’ll be Philae, all over again.
In the future, we’re told, humans will be visiting asteroids to study them for science and their potential for ice and minerals. You can imagine it’ll be a harrowing descent, but even just walking around on the surface will be dangerous when every step could throw an astronaut into an escape trajectory. They’ll need to learn lessons from rock climbers and Rorschach.
As we learned with Philae, landings on low mass objects is really tough. We’re going to need to get more practice and develop new techniques and technologies before we’re ready to add asteroid mining to our list of “stuff we just do, NBD”.
What are some unusual worlds you’d like humanity to visit? Put your suggestions in the comments below.