A pair of studies published in Science and Science Advances have helped identify that NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft would have sunk into the asteroid Bennu had the spacecraft not fired its thrusters immediately after collecting samples from the surface of the small planetary body in October 2020. The respective studies examined the loosely packed exterior of Bennu, comparing its surface to stepping into a pit of plastic balls that people of all ages enjoy. The paper in Science was led by Dr. David Lauretta, Principal Investigator of OSIRIS-REx and a Regents Professor at the University of Arizona, and the paper in Science Advances was led by Dr. David Walsh, a member of the OSIRIS-REx team from the Southwest Research Institute in Boulder, Colorado.Continue reading “OSIRIS-REx Would Have Sunk Deep into Asteroid Bennu if it Tried to Land”
Comet 67P/C-G may be tiny at just 2.5 miles (4 km) across, but its diverse landscapes and the processes that shape them astound. To say nature packs a lot into small packages is an understatement.
In newly-released images taken by Rosetta’s high-resolution OSIRIS science camera, the comet almost seems alive. Sunlight glints off icy boulders and pancaking sinkholes blast geysers of dust into the surrounding coma.
More than a hundred patches of water ice some 6 to 15 feet across (a few meters) dot the comet’s surface according to a new study just published in the journal Astronomy & Astrophysics. We’ve known from previous studies and measurements that comets are rich in ice. As they’re warmed by the Sun, ice vaporizes and carries away embedded dust particles that form the comet’s atmosphere or coma and give it a fuzzy appearance.
Not all that fine powder leaves the comet. Some settles back to the surface, covering the ice and blackening the nucleus. This explains why all the comets we’ve seen up close are blacker than coal despite being made of material that’s as bright as snow.
Scientists have identified 120 regions on the surface of Comet 67P/Churyumov-Gerasimenko that are up to ten times brighter than the average surface brightness. Some are individual boulders, while others form clusters of bright specks. Seen in high resolution, many appear to be boulders with exposures of ice on their surfaces; the clusters are often found at the base of overhanging cliffs and likely got there when cliff walls collapsed, sending an avalanche of icy rocks downhill and exposing fresh ice not covered by dark dust.
More intriguing are the isolated boulders found here and there that appear to have no relation to the surrounding terrain. Scientists think they arrived George Jetson style when they were jetted from the comet’s surface by the explosive vaporization of ice only to later land in a new location. The comet’s exceedingly low gravity makes this possible. Let that image marinate in your mind for a moment.
All the ice-glinting boulders seen thus far were found in shadowed regions not exposed to sunlight, and no changes were observed in their appearance over a month’s worth of observations.
“Water ice is the most plausible explanation for the occurrence and properties of these features,” says Antoine Pommerol of the University of Bern and lead author of the study.
How do we know it’s water ice and not CO2 or some other form of ice? Easy. When the observations were made, water ice would have been vaporizing at the rate of 1 mm per hour of solar illumination. By contrast, carbon monoxide or carbon dioxide ice, which have much lower freezing points, would have rapidly sublimated in sunlight. Water ice vaporizes much more slowly in comparison.
Lab tests using ice mixed with different minerals under simulated sunlight revealed that it only took a few hours of sublimation to produce a dust layer only a few millimeters thick. But it was enough to conceal any sign of ice. They also found that small chunks of dust would sometimes break away to expose fresh ice beneath.
“A 1 mm thick layer of dark dust is sufficient to hide the layers below from optical instruments,” confirms Holger Sierks, OSIRIS principal investigator at the Max Planck Institute for Solar System Research.
It appears then that Comet 67P’s surface is mostly covered in dark dust with small exposures of fresh ice resulting from changes in the landscape like crumbling cliffs and boulder-tossing from jet activity. As the comet approaches perihelion, some of that ice will become exposed to sunlight while new patches may appear. You, me and the Rosetta team can’t wait to see the changes.
Ever wonder how a comet gets its jets? In another new study appearing in the science journal Nature, a team of researchers report that 18 active pits or sinkholes have been identified in the comet’s northern hemisphere. These roughly circular holes appear to be the source of the elegant jets like those seen in the photo above. The pits range in size from around 100 to 1,000 feet (30-100 meters) across with depths up to 690 feet (210 meters). For the first time ever, individual jets can be traced back to specific pits.
In specially processed photos, material can be seen streaming from inside pit walls like snow blasting from a snowmaking machine. Incredible!
“We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,” said Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.
Similar to the way sinkholes form on Earth, scientists believe pits form when the ceiling of a subsurface cavity becomes too thin to support its own weight. With nothing below to hold it place, it collapses, exposing fresh ice below which quickly vaporizes. Exiting the hole, it forms a collimated jet of dust and gas.
The paper’s authors suggest three ways for pits to form:
* The comet may contain voids that have been there since its formation. Collapse could be triggered by either vaporizing ice or seismic shaking when boulders ejected elsewhere on the comet land back on the surface.
* Direct sublimation of pockets of volatile (more easily vaporized) ices like carbon dioxide and carbon monoxide below the surface as sunlight warms the dark surface dust, transferring heat below.
* Energy liberated by water ice changing its physical state from amorphous to its normal crystalline form and stimulating the sublimation of the surrounding more volatile carbon dioxide and carbon monoxide ices.
The researchers think they can use the appearance of the sinkholes to age-date different parts of the comet’s surface — the more pits there are in a region, the younger and less processed the surface there is. They point to 67P/C-G’s southern hemisphere which receives more energy from the Sun than the north and at least for now, shows no pit structures.
The most active pits have steep sides, while the least show softened contours and are filled with dust. It’s even possible that a partial collapse might be the cause of the occasional outbursts when a comet suddenly brightens and enlarges as seen from Earth. Rosetta observed just such an outburst this past April. And these holes can really kick out the dust! It’s estimated a typical full pit collapse releases a billion kilograms of material.
With Rosetta in great health and perihelion yet to come, great things lie ahead. Maybe we’ll witness a new sinkhole collapse, an icy avalanche or even levitating boulders!
67P/Churyumov-Gerasimenko certainly isn’t a comet that dreads sundown. Images acquired by the OSIRIS instrument aboard ESA’s Rosetta spacecraft in April 2015 reveal that some of the comet’s dust jets keep on firing even after the Sun has “set” across those regions. This shows that, as the comet continues to approach its August perihelion date, it’s now receiving enough solar radiation to warm deeper subsurface materials.
“Only recently have we begun to observe dust jets persisting even after sunset,” said OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research.
The image above was captured by OSIRIS on April 25 and shows active jets near the center, originating from shadowed areas on the comet’s smaller “head” lobe. The region is called Ma’at – see maps of 67P’s regions here and here.
(Also it looks kind of like an overexposed image of a giant angry lemming. But that’s pareidolia for you.)
It’s thought that the comet has now come close enough to the Sun – 220.8 million kilometers, at the time of this writing – that it can store heat below its surface… enough to keep the sublimation process going within buried volatiles well after it rotates out of direct solar illumination.
Source: ESA’s Rosetta blog
Host: Fraser Cain (@fcain)
Special Guest: Author Lee Billings, discussing his book “Five Billion Years of Solitude”(@LeeBillings / leebillings.com/)
Dr. Pamela Gay (cosmoquest.org / @starstryder)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Brian Koberlein (@briankoberlein)
Continue reading “Weekly Space Hangout – March 20, 2015: Lee Billings’ Five Billion Years of Solitude”
A particularly dramatic view of comet 67P/C-G due to the angle of solar illumination, this is a mosaic made from four images acquired by Rosetta’s NavCam on January 16, 2015, from a distance of 28.4 km (17.6 miles). The assembled image shows the larger “bottom” lobe of 67P, with a flat region called Imhotep along the left side and, on the lower right, the transition area stretching up to the comet’s smaller “head” lobe. Outgassing jets can be seen as faint streaks at the upper right, and ejected dust grains show up as bright specks above its surface.
Also in this view is one of 67P’s larger boulders, a somewhat pyramid-shaped rock dubbed “Cheops.” Can you spot it?
There it is!
One in a cluster of boulders on 67P’s “underside,” Cheops is about 45 meters wide and 25 meters high (148 x 82 feet).
When it was first observed in Rosetta images Cheops and the nearby cluster reminded scientists of the pyramids at Giza in Egypt, and so it was named for the largest of those pyramids, the Great Pyramid, a tomb for the pharaoh Cheops (the Hellenized name for Khufu) built around 2,550 BCE. (See another view of the Cheops cluster here.)
Scientists are still working to determine the nature of 67P’s boulders. It’s not yet known what they are made of or how they came to be where they are observed today. Did they fall into their current positions? Or were they exposed upwards from below as a result of the comet’s activity? And why do they have alternating rough and smooth areas on their surfaces?
“It almost looks as if loose dust covering the surface of the comet has settled in the boulder’s cracks. But, of course, it is much too early to be sure,” said OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany.
As comet 67P approaches perihelion over the course of the next six months we will get to see firsthand via Rosetta what sorts of changes occur to its surface features, including office-building-sized boulders like Cheops.
Also, for a quick look at some of 67P’s “vital stats” click here. (Added 1/22)
Source: ESA Rosetta blog
This week, history was made as the Rosetta mission’s Philae lander touched down on the surface of 67P/Churnyumov-Gerasimenko. Days before this momentous event took place, the science team presented some staggering pictures of the comet at a planetary conference in Tucson, Arizona, where guests were treated to the first color images taken by the spacecraft’s high-resolution camera.
Unfortunately for millions of space enthusiasts around the world, none of these exciting images were released to the public. In addition, much of the images taken of the comet over the past few months as Rosetta closed in on it have similarly not been released. This has led to demands for more openness, which in turn has focused attention on ESA’s image and data release policy.
Allowing scientists to withhold data for some period of time is not uncommon in planetary science. According to Jim Green, the director of NASA’s Planetary Science Division, a 6-month grace period is typical for principal investigator-led spacecraft. However, NASA headquarters can also insist that the principal investigator release data for key media events.
This has certainly been the case where the Curiosity and other Mars rover missions were concerned, not to mention the Cassini-Huygens mission. On many occasions, NASA chose to release images to the public almost immediately after they were obtained.
However, ESA has a different structure than NASA. It relies much more on contributions from member-states, whereas NASA pays for most of its instruments directly. Rosetta’s main mission camera – the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) – was developed by a consortium of institutes led by the Max-Planck-Institute for Solar System Research. As a result, ESA has less control over how information obtained by this specific camera is disseminated.
Journalist Eric Hand recently covered this imagery release dilemma in an article in Science, revealing that even scientists at Darmstadt, Germany this week — the location of ESA’s mission control for Philae’s landing — had not seen the science images that were being shared at the Planetary Science conference. Project scientist Matt Taylor was reduced to learning about the new results by looking at Twitter feeds on his phone.
Hand quoted Taylor as saying the decision when to publicly release images is a “tightrope” walk. And Hand also said some “ESA officials are worried that the principal investigators for the spacecraft’s 11 instruments are not releasing enough information, and many members of the international community feel the same way.”
Back in July, ESA responded to these calls for more information with a press release, in which they claimed that an “open-data” policy is not the norm for either ESA or NASA. Responding to the examples of the Mars rovers and Cassini-Huygens, which have been cited by critics for more openness, ESA countered with the Hubble Space Telescope, the Chandra X-Ray observatory, the MESSENGER mission to Mercury, and even some NASA Mars orbiters.
In these cases, they claimed, the data obtained was subject to a “proprietary period”, which also pertains to data from ESA’s Mars Express, XMM-Newton, and Rosetta missions. This period, they said, is typically 6-12 months, and “gives exclusive access to the scientists who built the instruments or to scientists who made a winning proposal to make certain observations.”
Nevertheless, there is still some criticism by those who think that releasing more images would be a positive gesture and not compromise any ESA scientist’s ability to conduct research.
As space blogger Daniel Fischer said in response to the ESA press release, “Who is writing scientific papers already about the distant nucleus that is just turning into a shape? And on the weekly schedule a sampling of these images is coming out anyway, with a few days delay… Presenting the approach images, say, one per day and with only hours delay would thus not endanger any priorities but instead give the eager public a unique chance to ‘join the ride’, just as they can with Cassini or the Mars rovers.”
In particular, a lot of criticism has been focused on the OSIRIS camera team, led by principal investigator Holger Sierks. Days before the Philae Lander put down on the comet, Cumbrian Sky:an amateur astronomer, space educator and image processor – wrote the following on his space blog
[The OSIRIS team’s] attitude towards the public, the media, and ESA itself has been one of arrogant contempt, and I have no doubt at all that their selfish behaviour has damaged the mission and the reputation and public image ESA. Their initial arguments that they had to keep images back to allow them to do their research no longer hold up now. They must have taken many hundreds of jaw droppingly detailed images by now, the images everyone has been looking forward to ever since ROSETTA launched a decade ago, so could easily release dozens of images which pose no risk to their work or careers, but they have released only a handful, and those have been the least-detailed, least-remarkable images they could find.
However, in Hand’s Science article, Sierks said that he feels the OSIRIS team has already provided a fair amount of data to the public. Currently, about one image is released a week – a rate that seems to Sierks to be more than adequate given that they are superior to anything before seen in terms of comet research.
Furthermore, Sierks claimed that other researchers, unaffiliated with the Rosetta team, have submitted papers based on these released images, while his team has been consumed with the daily task of planning the mission. After working on OSIRIS since 1997, Sierks feels that his team should get the first shot at using the data.
This echoes ESA’s July press release, which expressed support for their science teams to have first-crack any data obtained by their instruments. “Because no-one has ever been to 67P/C-G before,” it stated, “each new piece of data from Rosetta has the potential for a scientific discovery. It’s only fair that the instrument science teams have the first chance to make and assess those discoveries.”
The same press release also defended ESA’s decision not to release information from the navigation cameras more freely – which they do have control over. Citing overlap, they indicated that they want to “avoid undermining the priority of the OSIRIS team.”
Prior to Rosetta’s launch in 2004, an embargo of 6 months was set for all the instrument teams. ESA scientists have pointed out that mission documents also stipulate that instrument teams provide “adequate support” to ESA management in its communication efforts.
Mark McCaughrean, an ESA senior science adviser at ESTEC, is one official that believes these support requirements are not being met. He was quoted by Eric Hand in Science as saying, “I believe that [the OSIRIS camera team’s support] has by no means been adequate, and they believe it has,” he says. “But they hold the images, and it’s a completely asymmetric relationship.”
Luckily, ESA has released images of the surface of 67P and what it looked like for the Philae Lander and as it made its descent towards the comet. Additionally, stunning imagery from Rosetta’s navigation camera were recently released. In the coming days and weeks, we can certainly hope that plenty of more interesting images and exciting finds will be coming, courtesy of the Rosetta mission and its many contributors.
The long-awaited deployment of the Philae lander, currently “piggybacked” aboard ESA’s Rosetta spacecraft orbiting the nucleus of Comet 67P/Churyumov-Gerasimenko, will occur in less than a month and we now have our best look yet at the area now green-lighted for touchdown. The picture above, made from two images acquired by Rosetta’s OSIRIS imaging instrument, shows a 500-meter circle centered on “Site J,” a spot on the comet’s “head” carefully chosen by mission scientists as the best place in which Philae should land, explore, and ultimately travel around the Sun for the rest of its days. And as of today, it’s a GO!
Site J was selected from among five other possible sites and was chosen because of the relative safety of its surface, its accessibility to consistent solar illumination, and the scientific and observational data it can make available to Philae’s suite of onboard instruments.
“None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.
The mosaic above comprises two images taken by Rosetta’s OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) narrow-angle camera on Sept. 14 from a distance of about 30 km (18.6 miles). Image scale is 0.5 m/pixel.
As Comet 67P/CG continues toward perihelion its outgassing and sublimation jetting will undoubtedly increase, and Philae will be getting a front-row seat to the action.
“Site J is just 500-600 meters away from some pits and an area of comet outgassing activity,” said Holger Sierks, principal investigator for Rosetta’s OSIRIS camera from the Max Planck Institute for Solar System Research in Gottingen, Germany. “They will become more active as we get closer to the Sun.”
After completing a series of “Go/No-go” decisions by Rosetta’s flight dynamics team, Philae’s separation from Rosetta will occur on Nov. 12 at 08:35 GMT. It will land about seven hours later at around 15:30 GMT. Because of the distance to the comet and spacecraft — about 509 million km — confirmation of a successful touchdown won’t be received on Earth until 28 minutes and 20 seconds later. (And you thought Curiosity’s “seven minutes of terror” was nerve-wracking!)
The image of Comet 67P/Churyumov-Gerasimenko was taken by Rosetta’s OSIRIS narrow-angle camera on 3 August 2014 from a distance of 285 km. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“We’re at the comet! Yes,” exclaimed Rosetta Spacecraft Operations Manager Sylvain Lodiot, confirming the spacecraft’s historic arrival at Comet 67P/Churyumov-Gerasimenko during a live webcast this morning, Aug. 6, from mission control at ESA’s spacecraft operations centre (ESOC) in Darmstadt, Germany.
The European Space Agency’s (ESA) Rosetta comet hunter successfully reached its long sought destination after a flawless orbital thruster firing at 11 AM CEST to become the first spacecraft in history to rendezvous with a comet and enter orbit aimed at an ambitious long term quest to produce ground breaking science.
“Ten years we’ve been in the car waiting to get to scientific Disneyland and we haven’t even gotten out of the car yet and look at what’s outside the window,” Mark McCaughrean, senior scientific adviser to ESA’s Science Directorate, said during today’s webcast. “It’s just astonishing.”
“The really big question is where did we and the solar system we live in come from? How did water and the complex organic molecules that build up life get to this planet? Water and life. These are the questions that motivate everybody.”
“Rosetta is indeed the ‘rosetta stone’ that will unlock this treasure chest to all comets.”
Today’s rendezvous climaxed Rosetta’s decade long and 6.4 billion kilometers (4 Billion miles) hot pursuit through interplanetary space for a cosmic kiss with Comet 67P while speeding towards the inner Solar System at nearly 55,000 kilometers per hour.
The probe is sending back spectacular up close high resolution imagery of the mysterious binary, two lobed comet, merged at a bright band at the narrow neck of the celestial wanderer that looks like a ‘rubber ducky.’
“This is the best comet nucleus ever resolved in space with the sharpest ever views of the nucleus, with 5.5.meter pixel resolution,” said Holger Sierks, principal investigator for Rosetta’s OSIRIS camera from the Max Planck Institute for Solar System Research in Gottingen, Germany, during the webcast.
“We now see lots of structure and details. Lots of topography is visible on the surface. We see the nucleus and outgassing activity. The outbursts are seen with overexposed images. It’s really fantastic”
“There is a big depression on the head and 150 meter high cliffs, rubble piles, and also we see smooth areas and plains. The neck is about 1000 meters deep and is a cool area. There is outgassing visible from the neck.”
“We see a village of house size boulders. Some about 10 meters in size and bigger they vary in brightness. And some with sharp edges. We don’t know their composition yet.”
“We don’t understand how its created yet. That’s what we’ll find out in coming months as we get closer.”
“Rosetta has arrived and will get even closer. We’ll get ten times the resolution compared to now.”
“The comet is a story about us. It will be the key in cometary science. Where did it form? What does it tell us about the water on Earth and the early solar system and where it come from?”
Following the blastoff on 2 March 2004 tucked inside the payload fairing of an Ariane 5 G+ rocket from Europe’s spaceport in Kourou, French Guiana, Rosetta traveled on a complex trajectory.
It conducted four gravity assist speed boosting slingshot maneuvers, three at Earth and one at Mars, to gain sufficient velocity to reach the comet, Lodiot explained.
The 1.3 Billion euro robotic emissary from Earth is now orbiting about 100 kilometers (62 miles) above the comet’s surface, some 405 million kilometers (250 million mi.) from Earth, about half way between the orbits of Jupiter and Mars.
The main event today, Aug. 6, was to complete an absolutely critical thruster firing which was the last of 10 orbit correction maneuvers (OCM’s). It started precisely on time at 11:00 AM CEST/09:00 GMT/5:00 AM EST, said Lodiot. The signal was one of the cleanest of the entire mission.
The orbital insertion engine firing dubbed the Close Approach Trajectory – Insertion (CATI) burn was scheduled to last about 6 minutes 26 seconds. Confirmation of a successful burn came some 28 minutes later.
“We’re at the comet! Yes,” Lodiot excitedly announced live whereupon the crowd of team members, dignitaries and journalists at ESOC erupted in cheers.
For the next 17 months, the probe will escort comet 67P as it loops around the Sun towards perihelion in August 2015 and then continue along on the outbound voyage towards Jupiter.
ESA’s incredibly bold mission will also deploy the three-legged piggybacked Philae lander to touch down and drill into and sample its incredibly varied surface a little over three months from now.
Together, Rosetta and Philae are equipped with a suite of 21 science instruments to conduct an unprecedented investigation to characterize the 4 km wide (2.5 mi.) comet and study how the pristine frozen body composed of ice and rock is transformed by the warmth of the Sun.
Comets are believed to have delivered a vast quantity of water to Earth. They may have also seeded Earth with organic molecules.
Rosetta and Philae will also search for organic molecules, nucleic acids and amino acids, the building blocks for life as we know it by sampling and analyzing the comets nucleus and coma cloud of gas and dust.
“The first coma sampling could happen as early as next week,” said Matt Taylor, ESA’s Rosetta project scientist on the webcast.
“Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects.”
After thoroughly mapping the comet, the team will command Rosetta to move even lower to 50 km altitude and then even lower to 30 km and less.
The scientists and engineers will search for up to five possible landing sites for Philae to prepare for the touchdown in mid-November 2014.
“We want to characterize the nucleus so we can land in November,” said Taylor. “We will have a ringside along with the comet as it moves inwards to the sun and then further out.”
Studying comets will shed light on the history of water and life on Earth.
“We are going to places we have never been to before,” said Jean-Jacques Dordain, ESA’s Director General during the webcast.
“We want to get answers to questions to the origin to water and complex molecules on Earth. This opens up even more new questions than answers.”
Watch for updates.
Stay tuned here for Ken’s continuing Rosetta, Curiosity, Opportunity, Orion, SpaceX, Boeing, Orbital Sciences, commercial space, MAVEN, MOM, Mars and more Earth and Planetary science and human spaceflight news.
Read my Rosetta series here:
WOW! We’re really getting to the good stuff now! This is no computer-generated shape model, this is the real deal: the double-lobed nucleus of Comet 67P/C-G, as imaged by Rosetta’s OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) narrow-angle camera on Tuesday, July 29. At the time just about a week away from making its arrival, ESA’s spacecraft was 1,950 km (1,211 miles) from the comet when this image was taken. (That’s about the distance between Providence, Rhode Island and Miami, Florida… that’s one fancy zoom lens, Rosetta!)
This latest image reveals some actual surface features of the 4-km-wide comet, from a few troughs and mounds to the previously-noted bright band around the “neck” connecting the two lobes. The resolution in the July 29 OSIRIS image is 37 meters per pixel.
Since Rosetta is quickly closing the gap between itself and the comet we can only expect better images to come in the days ahead, so stay tuned — this is going to be an exciting August!
Image credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA