Philae landed nearly vertically on its side with one leg up in outer space. Here we see it in relation to the panoramic photos taken with the CIVA cameras. Credit: ESA
No, scientists haven’t found Philae yet. But as they churn through the scientific data on the comet lander, more information is emerging about the crazy landing last month that included three touchdowns and an incredible two hours of drifting before Philae came to rest in a relatively shady spot on the surface.
Among the latest: the tumbling spacecraft “collided with a surface feature” shortly after its first landing, perhaps grazing a crater rim with one of its legs. This information comes from an instrument called ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) that monitors magnetic fields. The instrument is now being used to track down the spacecraft.
ROMAP’s usual role is to look at the comet’s magnetic field as it interacts with the solar wind, but the challenge is the orbiter (Rosetta) and lander both create tiny ones of their own due to the magnetic circuitry. Usually this data is removed to see what the comet’s environment is like. But during the landing, ROMAP was used to track Philae’s descent.
Four images of Comet 67P/Churyumov–Gerasimenko taken on Nov. 30, 2014 by the orbiting Rosetta spacecraft. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Philae was supposed to fire harpoons to secure itself to the surface when it touched down at 3:34 p.m. UTC (10:34 a.m. EST) Nov. 12, but the mechanism failed. ROMAP’s data then shows the spin rate increasing, with the lander turning at one rotation every 13 seconds.
The grazing collision happened at 4:20 pm. UTC (11:20 a.m. EST), making the rotation decrease to once every 24 seconds. Then the final two touchdowns happened around 5:25 p.m. UTC (12:25 p.m. EST) and 5:31 p.m. UTC (12:31 p.m. EST). Controllers hope they can figure out exactly where Philae arrived once they look at data from ROMAP, CONSERT and other instruments on the lander.
Philae is now hibernating because there isn’t enough sunlight in its landing spot to recharge its battery through the solar panels. Rosetta, meanwhile, continues orbiting 67P and sending back pictures of the comet as it draws closer to the Sun, including the image you see further up in this blog post, released today (Dec. 2) a few days after it was taken in space.
Gas and dust stream from Comet 67P/Churyumov–Gerasimenko in this mosaic from the Rosetta spacecraft taken Nov. 20, 2014. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Get a load of those streaks! Rosetta’s comet is picking up in activity as it moves ever closer to the Sun, sending out a steady stream of gas and dust captured in this image released today (Nov. 26). It’s also possible that there might be an “atmosphere” developing around the comet, although the images aren’t clear on if that’s an artifact of Rosetta itself.
As the European Space Agency scurries to find the final resting place of the Philae lander, Rosetta continues normal operations above the comet and will keep tracking it through 2015. Rosetta is the first orbiter to stick around near a comet, which will allow scientists an unprecedented chance to see a comet change from up close as the Sun’s heat and particles affect it. Could there be an atmosphere starting up?
“At the bottom of the mosaic, the non-illuminated part of the comet stands out as a silhouette against the broader diffuse emission coming from the comet’s coma,” ESA stated. “There are hints of a diffuse ‘atmosphere’ close to the surface of the comet seen along the illuminated edges, but this could be due to scattering in the NAVCAM optics. The large number of small white blobs in the image are likely specks of dust or other small objects in the vicinity of the comet.”
Here’s the same image below, but slightly oversatured to bring out those streaks. It’ll be fun to see the changes at 67P over the next few months, and ESA is still holding out hope that Philae will wake up in a few months once enough sunlight reaches its shady spot. If that happens, scientists can then get an extreme close-up of 67P’s activity as well.
A mosaic of Comet 67P/Churyumov–Gerasimenko taken by the Rosetta spacecraft Nov. 20, with more exposure and contrast to bring out jets erupting from the comet’s surface. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
A 3-D image of Comet 67P/Churyumov–Gerasimenko taken from the Philae lander as it descended. The picture is a combination of two images from the Rosetta Lander Imaging System (ROLIS) taken about an hour before landing at 10:34 a.m. EST (3:34 p.m. UTC) on Nov. 12, 2014. Credit: ESA/Rosetta/Philae/ROLIS/DLR
The first soft comet landing Nov. 12 showed us how space missions can quickly drift to the unexpected. Philae’s harpoons to secure it failed to fire, and the spacecraft drifted for an incredible two hours across Comet 67P/Churyumov–Gerasimenko before coming to rest … somewhere. But where? And can the orbiting Rosetta spacecraft find it?
That’s been the obsession of the European Space Agency for the past couple of weeks. Controllers have pictures from Philae during its descent and brief science operations on the surface. They’ve managed to capture the little lander in incredible photographs from Rosetta. But the key to finding Philae will likely come from a different experiment altogether.
The experiment is called the Comet Nucleus Sounding Experiment by Radio wave Transmission (CONSERT) and is a piece of work between both lander and orbiter. Rosetta sent radio signals to Philae on the surface to get a better sense of what the insides of 67P are made of. But it turns out it can also be used to pinpoint the lander.
ESA recently released a landing zone of where, based on CONSERT data, it believes the lander came to rest. The next step will be to get the Rosetta spacecraft to examine the area in high-definition.
An estimation of Philae’s landing site on Comet 67P/Churyumov–Gerasimenko, based on data from the Comet Nucleus Sounding Experiment by Radio wave Transmission (CONSERT) experiment. Credit: ESA/Rosetta/Philae/CONSERT
“By making measurements of the distance between Rosetta and Philae during the periods of direct visibility between orbiter and lander, as well as measurements made through the core, the team have been able to narrow down the search to the strip presented in the image shown above,” ESA stated. “The determination of the landing zone is dependent on the underlying comet shape model used, which is why there are two candidate regions marked.”
Finding Philae is not only a goal to fulfill curiosity, but also to learn more about the comet itself. The team needs to know where the lander is sitting before they can fully analyze the CONSERT data, they said. So the search continues for the hibernating lander, which right now is in a shady spot and unable to transmit status updates since it can’t get enough sunlight to recharge. (This could change as 67P gets closer to the Sun, but nobody knows for sure.)
Rosetta, meanwhile, is in perfect health and continues to transmit incredible pictures of the comet, such as this one below released a couple of days ago. The montage you see includes the zone where Philae was supposed to have touched down, but it will take higher-resolution images from the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) to get a better look.
A montage of four images of Comet 67P/Churyumov–Gerasimenko taken by the Rosetta spacecraft on Nov. 20, 2014. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
The Rosetta spacecraft takes a selfie Oct. 7 with its target, 67P/Churyumov–Gerasimenko, from an altitude of about 9.9 miles (16 kilometers). Credit: ESA/Rosetta/Philae/CIVA
With the Philae mission down on the comet and preliminary science results coming from its brief science surge on the surface, little has been said about the delivery vehicle. But while Philae is in hibernation, the Rosetta spacecraft remains quietly in orbit around Comet 67P/Churyumov–Gerasimenko for what will prove to be a dramatic 2015.
Should the orbiter remain healthy, it will be the first to be a “comet escort” — to watch a comet changing from up close as the celestial body draws closer to the Sun. And to stay out of the debris field, Rosetta will have some fancy footwork to perform in the next few months, says the European Space Agency (ESA).
“Burns” with the comet are planned on Saturday (Nov. 22) and Wednesday (Nov. 26) to bring it up about 30 kilometers (19 miles) above, and then it will scoot down closer to about 20 kilometers (12.5 miles) on Dec. 3. Rosetta will remain in this orbit for a while to look at the comet’s nucleus, as well as to measure plasma, dust and gas that is expected to increase as the comet gets closer to the Sun.
Rosetta will stay as close to 67P as possible, but if activity heats up to an unacceptable risk, it will jump to a “high-activity” trajectory that will keep it away from the worst of the debris. And it’s also going to keep an ear out for Philae, just in case more sunlight on the comet ends up recharging the hibernating lander’s battery. “Early next year, Rosetta will be switched into a mode that allows it to listen periodically for beacon signals from the surface.,” ESA wrote.
There has been some discussion about the magnitude of Philae’s success given that it did land on the comet as planned, but the harpoons (which had travelled a decade in space at that point) did not fire on to the surface as planned. This meant that the lander drifted for about two hours before settling far from its prime landing spot, mostly outside of the sunlight it needs to recharge its batteries.
Our last panorama from Philae? This image was taken with the CIVA camera; at center Philae has been added to show its orientation on the surface. Credit: ESA
And we have touchdown! This is what the feet of the Philae lander experienced as the spacecraft touched down on its cometary destination last week. You can hear the brief sound from the Cometary Acoustic Surface Sounding Experiment (CASSE) above. What’s even cooler is the scientific data that short noise reveals.
CASSE is embedded in the three legs of Philae and recorded the first of three landings for the spacecraft, which bounced for about two hours before coming to rest somewhere on Comet 67P/Churyumov–Gerasimenko (where is still being determined).
About that first touchdown: “The Philae lander came into contact with a soft layer several centimetres thick. Then, just milliseconds later, the feet encountered a hard, perhaps icy layer on 67P/Churyumov-Gerasimenko,” stated German Space Agency (DLR) researcher Klaus Seidensticker. He is the lead for the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME), which includes CASSE.
CASSE also recorded information from the lander’s feet from Philae’s final resting spot, and transmitted information about the MUlti PUrpose Sensor (MUPUS) as the latter instrument drilled into the surface. Other instruments on SESAME found no dust particles nearby the lander (which scientists say means the landing site is quiescent) and also sensed water ice beneath the lander.
Philae is now in hibernation as its final resting spot does not include a lot of sunlight to recharge the solar panels, but the researchers are hoping that more energy might be available as 67P draws closer to the Sun in 2015. The orbiting Rosetta spacecraft is continuing to collect data on the comet.
Philae's MUPUS probe took temperature measurements and hammered into the surface at the landing site to discover the lander alighted on some very hard ice. Credit: ESA
An uncontrolled, chaotic landing. Stuck in the shadow of a cliff without energy-giving sunlight. Philae and team persevered. With just 60 hours of battery power, the lander drilled, hammered and gathered science data on the surface of comet 67P/Churyumov-Gerasimenko before going into hibernation. Here’s what we know.
Despite appearances, the comet’s hard as ice. The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument hammered a probe as hard as they could into 67P’s skin but only dug in a few millimeters:
Close-up of the first touchdown site before Philae landed (left) and after clearly shows the impressions of its three footpads in the comet’s dusty soil. At the final landing site, it’s believed that Times are CST. Philae’s 3.3 feet (1-m) across. Credit: ESA
“Although the power of the hammer was gradually increased, we were not able to go deep into the surface,” said Tilman Spohn from the DLR Institute of Planetary Research, who leads the research team. “If we compare the data with laboratory measurements, we think that the probe encountered a hard surface with strength comparable to that of solid ice,” he added. This shouldn’t be surprising, since ice is the main constituent of comets, but much of 67P/C-G appears blanketed in dust, leading some to believe the surface was softer and fluffier than what Philae found.
This finding was confirmed by the SESAME experiment (Surface Electrical, Seismic and Acoustic Monitoring Experiment) where the strength of the dust-covered ice directly under the lander was “surprisingly high” according to Klaus Seidensticker from the DLR Institute. Two other SESAME instruments measured low vaporization activity and a great deal of water ice under the lander.
As far as taking the comet’s temperature, the MUPUS thermal mapper worked during the descent and on all three touchdowns. At the final site, MUPUS recorded a temperature of –243°F (–153°C) near the floor of the lander’s balcony before the instrument was deployed. The sensors cooled by a further 10°C over a period of about a half hour:
The location of Philae’s first touchdown on the surface of Comet 67P/C-G. Although covered in dust in many areas, Philae found strong evidence for firm ice beneath the comet’s surface. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“We think this is either due to radiative transfer of heat to the cold nearby wall seen in the CIVA images or because the probe had been pushed into a cold dust pile,” says Jörg Knollenberg, instrument scientist for MUPUS at DLR. After looking at both the temperature and hammer probe data, the Philae team’s preliminary take is that the upper layers of the comet’s surface are covered in dust 4-8 inches (10-20 cm), overlaying firm ice or ice and dust mixtures.
The ROLIS camera (ROsetta Lander Imaging System) took detailed photos during the first descent to the Agilkia landing site. Later, when Philae made its final touchdown, ROLIS snapped images of the surface at close range. These photos, which have yet to be published, were taken from a different point of view than the set of panorama photos already received from the CIVA camera system.
During Philae’s active time, Rosetta used the CONSERT (COmet Nucleus Sounding Experiment by Radio wave Transmission) instrument to beam a radio signal to the lander while they were on opposite sides of the comet’s nucleus. Philae then transmitted a second signal through the comet back to Rosetta. This was to be repeated 7,500 times for each orbit of Rosetta to build up a 3D image of 67P/C-G’s interior, an otherworldly “CAT scan” as it were. These measurements were being made even as Philae lapsed into hibernation. Deeper down the ice becomes more porous as revealed by measurements made by the orbiter.
Rosetta’s Philae lander includes a carefully selected set of instruments to analyze a comet’s surface. Credit: ESA, Composite – T.Reyes
The last of the 10 instruments on board the Philae lander to be activated was the SD2 (Sampling, Drilling and Distribution subsystem), designed to provide soil samples for the COSAC and PTOLEMY instruments. Scientists are certain the drill was activated and that all the steps to move a sample to the appropriate oven for baking were performed, but the data right now show no actual delivery according to a tweet this morning from Eric Hand, reporter at Science Magazine. COSAC worked as planned however and was able to “sniff” the comet’s rarified atmosphere to detect the first organic molecules. Research is underway to determine if the compounds are simple ones like methanol and ammonia or more complex ones like the amino acids.
Stephan Ulamec, Philae Lander manager, is confident that we’ll resume contact with Philae next spring when the Sun’s angle in the comet’s sky will have shifted to better illuminate the lander’s solar panels. The team managed to rotate the lander during the night of November 14-15, so that the largest solar panel is now aligned towards the Sun. One advantage of the shady site is that Philae isn’t as likely to overheat as 67P approaches the Sun en route to perihelion next year. Still, temperatures on the surface have to warm up before the battery can be recharged, and that won’t happen until next summer.
Let’s hang in there. This phoenix may rise from the cold dust again.
A 3-D reconstruction of the Rosetta comet (67P/Churyumov-Gerasimenko) in a 2003 model from the Hubble Space Telescope. Credit: NASA, ESA and Philippe Lamy (Laboratoire d'Astronomie Spatiale)
Okay, let’s take a deep breath about Rosetta and remember just how far we’ve come since the mission arrived at its target comet in August. Lately we’ve been focused on reporting on the Philae landing, but remember how we barely knew how the comet looked until this summer? How much of a surprise the rubber duckie shape was to us?
This Hubble Space Telescope model from 2003 shows us why. From afar, Comet 67P/Churyumov-Gerasimenko is a tiny object to image, even for the NASA probe’s powerful lens. Back then, the telescope was tasked with examining the comet to look at its size and shape to better design the Philae lander spacecraft. And the model reveals no duckie; it looks more like a sombrero from some angles.
The main concern of scientists back then was redirecting Rosetta to a new target when its original comet (46P/Wirtanen) fell out of reach due to a launch delay. 67P was bigger and had a higher gravity, requiring scientists to make adjustments to Philae before landing, according to the release. So Hubble sprung into action to look at 67P. Below are the release images from that time.
A 2003 illustration of Comet 67P/Churyumov-Gerasimenko based on Hubble Space Telescope observations. Credit: NASA, ESA and Philippe Lamy (Laboratoire d’Astronomie Spatiale)
And here’s a fun quote from 2003 that finally came last Wednesday, when Philae touched down for its (sadly brief, so far) mission on the comet: “Although 67P/C-G is roughly three times larger than the original Rosetta target, its elongated shape should make landing on its nucleus feasible, now that measures are in place to adapt the lander package to the new configuration before next year’s launch,” stated Philippe Lamy of the Space Astronomy Laboratory (Laboratoire d’Astronomie Spatiale) in France.
We’ve sure come a long way since then. Below are some of the pictures Rosetta caught of 67P as it made its approach to its target this year, after a decade flying through space. While Philae is in what could be permanent hibernation, Rosetta is orbiting, working well and expected to keep up observations when the comet draws closer to the sun in 2015.
Animation of Comet 67P/Churyumov-Gerasimenko as seen by Rosetta on June 27-28, 2014Comet 67P/C-G photographed on July 14, 2014 from a distance of approximately 12 000 km. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDARaw pixelated image of the comet (left) and after smoothing. Credit: ESAComet 67P/Churyumov-Gerasimenko at 621 miles (1,000 km) on August 1. Wow! Look at that richly-textured surface. This photo has higher resolution than previous images because it was taken with Rosetta’s narrow angle camera. The black spot is an artifact. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAPhoto of Comet 67P/C-G taken by Rosetta on August 6, 2014. Credit: ESA
Images from the Rosetta spacecraft show Philae drifting across the surface of its target comet during landing Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Wow! New images released from the Rosetta spacecraft orbiting Comet 67P/Churyumov–Gerasimenko show the spacecraft coming in for its (first) landing on Wednesday (Nov. 12). “The mosaic comprises a series of images captured by Rosetta’s OSIRIS camera over a 30 minute period spanning the first touchdown,” wrote the European Space Agency in a blog post today (Monday).
This is just the latest in a series of images coming from the orbiting Rosetta spacecraft showing the Philae lander coming in for its rendezvous with 67P. A major next step for the mission will be figuring out where the lander actually came for a rest, but there’s plenty of data from both Rosetta and Philae to comb through for this information, ESA said.
What’s known for sure is Philae made three touchdowns on the comet — making history as humanity’s first soft-lander on such an object — stopping in a shady area that will make recharging its solar panels difficult. The spacecraft is in hibernation as of Friday (Nov. 14) and scientists are really, really hoping it’s able to charge up for another science session soon. Rosetta, meanwhile, is hard at work above and will continue to follow the comet in 2015.
In case you missed it, below are some of the pictures over the last few days that could be used to help pinpoint the landing location.
A still of the Philae spacecraft bouncing off Comet 67P/Churyumov–Gerasimenko in an animation of Rosetta spacecraft images. The image was taken Nov. 12, 2014, at 10:35 a.m. EDT (3:35 p.m. UTC). Credit: ESA/Rosetta/NAVCAM; pre-processed by Mikel CananiaOur last panorama from Philae? This image was taken with the CIVA camera; at center Philae has been added to show its orientation on the surface. Credit: ESAThe animated image below provides strong evidence that Philae touched down for the first time almost precisely where intended. The animation comprises images recorded by Rosetta’s navigation camera as the orbiter flew over the (intended) Philae landing site on November 12th. The dark area is probably dust raised by the craft on touchdown. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Artist's impression (not to scale) of the Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov–Gerasimenko. Credit: ESA–C. Carreau/ATG medialab.
What price do you put on scientific discovery? From the way Twitter lit up last week when the Philae spacecraft touched down on Comet 67P/Churyumov–Gerasimenko — it was a top-trending topic for a while — it appears there’s a lot of discussion going on about the Rosetta mission and its value to humanity.
A recent infographic (which you can see below) points out that the Rosetta mission, which included the now-hibernating Philae lander, cost as much as about four Airbus 380 jetliners. Is US$1.75 billion (€1.4 billion) a bargain for letting us explore further into the universe, or could the money have been better-served elsewhere?
This is a question often brought up about the value of space exploration, or what is called “blue-sky” research in general. The first developers of lasers, for example, could not have predicted how consumers would use them millions of times over to watch DVDs and Blu-Rays. Or in a more practical use, how medical lasers are used today for surgeries.
An infographic of Rosetta spacecraft spending. Credit: Scienceogram.org (infographic), ESA/Rosetta/NAVCAM (comet image), ESA (Rosetta graphic), ESA/Airbus (data), Scienceogram.org (other data).
“Like a lot of blue-skies science, it’s very hard to put a value on the mission,” wrote Scienceogram.org, the organization that produced the infographic. “First, there are the immediate spin-offs like engineering know-how; then, the knowledge accrued, which could inform our understanding of our cosmic origins, amongst other things; and finally, the inspirational value of this audacious feat in which we can all share, including the next generation of scientists.”
To put the value of the Rosetta mission in more everyday terms, Scienceogram points out that the comet landing cost (per European citizen and per year between 1996 and 2015) was less than half the ticket price for Interstellar. That said, it appears that figure does not take into account inflation, so the actual cost per year may be higher.
The Rosetta spacecraft is still working well and is expected to observe its target comet through 2015. The Philae lander did perform the incredible feat of landing on 67P on Wednesday, but it ended up in a shadowy spot that prevented it from gathering sunlight to stay awake. The lander is now in hibernation, perhaps permanently, but scientists have reams of data from the lander mission to pore over.
It’s been said that Rosetta, in following 67P as it gets closer to the Sun, will teach us more about cometary behavior and the origins of our Solar System. Is the mission and its social-media-sensation pictures worth the price? Let us know in the comments. More information on the infographic (and the spreadsheet of data) are available here.
