Jet activity on Comet 67P/C-G imaged on Jan. 31 and Feb. 3, 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. Edit by Jason Major.
First off: no, comet 67P/Churyumov-Gerasimenko is not about to explode or disintegrate. But as it steadily gets nearer to the Sun the comet’s jets are getting more and more active and they’re putting on quite a show for the orbiting Rosetta spacecraft! Click the image for a jeterrific hi-res version.
The images above were captured by Rosetta’s NavCam on Jan. 31 and Feb. 3 from a distance of about 28 km (17 miles). Each is a mosaic of four separate NavCam acquisitions and they have been adjusted and tinted in Photoshop by yours truly to further enhance the jets’ visibility. (You can view the original image mosaics and source frames here and here.)
These dramatic views are just a hint at what’s in store; 67P’s activity will only be increasing in the coming weeks and months and, this weekend, Rosetta will be swooping down for an extreme close pass over its surface!
Detail of 67P from the Feb. 3 NavCam image
This Saturday, Feb. 14, Rosetta will be performing a very close pass of the comet’s nucleus, soaring over the Imhotep region at an altitude of only 6 km (3.7 miles) at 12:41 UTC. This will allow the spacecraft to closely image the comet’s surface, as well as investigate the behavior of its jets and how they interact with its developing coma.
“The upcoming close flyby will allow unique scientific observations, providing us with high-resolution measurements of the surface over a range of wavelengths and giving us the opportunity to sample – taste or sniff – the very innermost parts of the comet’s atmosphere,” said Rosetta project scientist Matt Taylor.
UPDATE: Here’s an image of 67P captured by Rosetta on Feb. 6 from a distance of 124 km (77 miles) as it moved into a higher orbit in preparation of its upcoming close pass. It’s the first single-frame image of the comet since leaving bound orbits.
Rosetta will dance close to 67P on Valentine's Day coming to within 3.7 miles of the comet. Credit: Bob King
Who doesn’t like to snuggle up with their Valentine on Valentine’s Day? Rosetta will practically whisper sweet nothings into 67P’s ear on February 14 when it swings just 3.7 miles (6 km) above its surface, its closest encounter yet.
Rosetta had been orbiting the comet at a distance of some 16 miles (26 km) but beginning yesterday, mission controllers used the spacecraft’s thrusters to change its orbit in preparation for the close flyby. First, Rosetta will move out to a distance of roughly 87 miles (140 km) from the comet this Saturday before swooping in for the close encounter at 6:41 a.m. CST on Feb. 14. Closest approach happens over the comet’s larger lobe, above the Imhotep region.
The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine’s Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau with additions by the author
The close encounter will provide opportunities for Rosetta’s science instruments to photograph 67P’s surface at high resolution across a range of wavelengths as well as get a close sniff of what’s inside its innermost coma or developing atmosphere. Scientists will also be looking closely at the outflowing gas and dust to see how it evolves during transport from the comet’s interior to the coma and tail.
As Rosetta swoops by its view of the comet will continuously change. Instruments will collect data on how 67P’s dust grains reflect light across a variety of orbital perspectives – from shadowless lighting with the Sun at the orbiter’s back to slanted lighting angles – to learn more about its properties.
The Imhotep region of comet 67P features a large, relatively smooth region and a smattering of large boulders. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam
“After this close flyby, a new phase will begin, when Rosetta will execute sets of flybys past the comet at a range of distances, between about 15 km (9 miles) and 100 km (62 miles),” said Sylvain Lodiot, ESA’s spacecraft operations manager.
During some of the close flybys, Rosetta trajectory will be almost in step with the comet’s rotation, allowing the instruments to monitor a single point on the surface in great detail as it passes by.
Helpful animation of how ESA mission controllers are changing Rosetta’s orbit to ready the probe for the Valentine’s Day flyby.
Perihelion, when the comet arcs closest to the Sun at a distance of 115.6 million miles (186 million km), occurs on August 13. Activity should be reaching its peak around that time. Beginning one month before, the Rosetta team will identify and closely examine one of the comet’s jets in wickedly rich detail.
“We hope to target one of these regions for a fly-through, to really get a taste of the outflow of the comet,” said Matt Taylor, ESA’s Rosetta project scientist.
A new jet issues from a fissure in the rugged, dusty surface of Rosetta's comet. Credit: ESO/Rosetta/Navcam
It only makes sense. Sunlight heats a comet and causes ice to vaporize. This leads to changes in the appearance of surface features. For instance, the Sun’s heat can gnaw away at the ice on sunward-facing cliffs, hollowing them out and eventually causing them to collapse in icy rubble. Solar heating can also warm the ice that’s beneath the surface.
When it becomes a vapor, pressure can build up, cracking the ice above and releasing sprays of gas and dust as jets. New images compared to old suggest the comet’s surface is changing as it approaches the Sun.
Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I’ve labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam
Recent photos taken by the Rosetta spacecraft reveal possible changes on the surface of 67P/Churyumov-Gerasimenko that are fascinating to see and contemplate. In a recent entry of the Rosetta blog, the writer makes mention of horseshoe-shaped features in the smooth neck region of the comet called “Hapi”. An earlier image from Jan. 8 may show subtle changes in the region compared to a more recent image from Jan. 22. We’ll get to those in a minute, but there may be examples of more vivid changes.
Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month’s time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam
I did some digging around and found what appears to be variations in terrain between photos of the same Hapi region on Dec. 9 and Jan.8. Just as the other writer took care to mention, viewing angle and lighting are not identical in the images. That has to be taken into account when deciding whether a change in a feature is real or due to change in lighting or perspective.
Side by side comparison of the two image from Dec. 9, 2014 (left) and Jan. 8, 2015. Credit: ESA/Rosetta/Navcam
But take a look at those cracks in the December image that appear to be missing in January’s. The change, if real, is dramatic. If they did disappear, how? Are they buried in dust released by jets that later drifted back down to the surface?
Comparison of Jan. 22 and Jan. 9 photos of the “horseshoes” or depressions in 67P’s Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam
Now back to those horseshoe features. Again, the viewing angles are somewhat different, but I can’t see any notable changes in the scene. Perhaps you can. While comets are expected to change, it’s exciting when it seems to be happening right before your eyes.
Four-image mosaic shows the comet overall on January 22 from a distance of 17.4 miles (28 km) from its center. The larger of the two lobes is at left; Hapi is the smooth region at the transition between the lobes. Credit: ESA/Rosetta/Navcam
A Fissure spanning over 100 meters across the neck of Rosetta's comet 67P raises the question of if or when will the comet breakup. The fissure is part of released studies by Rosetta scientists in the Journal Science (Image Credits: ESA/Rosetta, Illustration, T.Reyes)
Not all comets break up as they vent and age, but for Rosetta’s comet 67P, the Rubber Duckie comet, a crack in the neck raises concerns. Some comets may just fizzle and uniformly expel their volatiles throughout their surfaces. They may become like puffballs, shrink some but remain intact.
Comet 67P is the other extreme. The expulsion of volatile material has led to a shape and a point of no return; it is destined to break in two. Songwriter Neil Sedaka exclaimed, “Breaking Up is Hard to Do,” but for comets this may be the norm. The fissure is part of the analysis in a new set of science papers published this week.
Top left: The Hathor cliff face is to the right in this view. The aligned linear structures can be clearly seen. The smooth Hapi region is seen at the base of the Hathor cliff. Boulders are prevalent along the long axis of the Hapi region. Bottom left and right: Crack in the Hapi region. The left panel shows the crack (indicated by red arrows) extending across Hapi and beyond. The right panel shows the crack where it has left Hapi and is extending into Anuket, with Seth at the uppermost left and Hapi in the lower left. (Credit: ESA/Rosetta)
The images show a fissure spanning a few hundred meters across the neck of the two lobe comet. The fissure is just one of the many incredible features on Comet 67P and is reported in research articles released in the January 22, 2015, edition of the journal Science.
What it means is not certain, but Rosetta team scientists have stated that flexing of the comet might be causing the fissure. As the comet approaches the Sun, the solar radiation is raising the temperature of the surface material. Like all materials, the comet’s will expand and contract with temperature. And diurnal (daily) changes in the tidal forces from the Sun is a factor, too.
An image sequence from the Navcam of the Rosetta spacecraft (right) is shown beside a simulation. Further work on the interaction of comets with solar radiation will include computer models that utilize Rosetta data to reveal how comet nuclei evolve over time – over many orbits of the Sun- and break up. Peanut, rubber-duck, potatoes or just round-shaped comet nuclei likely result from combinations of rotation, changes in rotation, spin rate, composition and internal structure, as a nucleus interacts with the Sun over many orbits. (Credits: ESA/Rosetta, Illustration – J.Schmidt)
The crack, or fissure, could spell the beginning of the end for comet 67P/Churyumov–Gerasimenko. It is located in the neck area, in the region named Hapi, between the two lobes that make 67P appear so much like a Rubber Duck from a distance. The fissure could represent a focal point of many properties and forces at work, such as the rotation rate and axis – basically head over heels of the comet. The fissure lies in the most active area at present, and possibly the most active area overall. Though the Hapi region appears to receive nearly constant sunlight, at this time, Rosetta measurements (below) show otherwise – receiving 15% less sunlight than elsewhere.
Left: A map looking at the northern (right-hand rule, positive,) pole of 67P showing the total energy received from the Sun per rotation on 6 August 2014. The base of the neck (Hapi) receives ~15% less energy than the most illuminated region, 3.5 × 106 J m-2 (per rotation). If self-heating were not included, the base of the neck would receive ~30% less total energy. Right: Similar to the left panel but showing total energy received over an entire orbital period in J m-2 (per orbit). (Credit:ESA/Journal Science Article, Figure 5)
Sunlight and heating are major factors and the neck likely experiences the greatest mechanical stresses – internal torques – from heating or tidal forces from the sun as it rotates and approaches perihelion. Rosetta scientists are still not certain whether 67P is two bodies in contact – a contact binary – or a shape that formed from material expelled about the neck area leading to its narrowing.
Fragmentation of comets is common. Many sungrazers are broken up by thermal and tidal stresses during their perihelions. At top, an image of the comet Shoemaker-Levy 9 (May 1994) after a close approach with Jupiter which tore the comet into numerous fragments. An image taken by Andrew Catsaitis of components B and C of Comet 73P/Schwassmann–Wachmann 3 as seen together on 31 May 2006 (Credit: NASA/HST, Wikipedia, A. Catsaitis)
The Philae lander’s MUPUS thermal sensor measured a temperature of –153°C (–243°F) at the landing site, while VIRTIS, an instrument on the primary spacecraft Rosetta, has measured -70°C (-94°F) at present. These temperatures will rise as perihelion is reached on August 13, 2015, at a distance of 1.2432 A.U. (24% further from the Sun than Earth). At present – January 23rd – 67P is 2.486 A.U. from the Sun (2 1/2 times farther from the Sun than Earth). While not a close approach to the Sun for a comet, the Solar radiation intensity will increase by 4 times between the present (January 2014) and perihelion in August.
Hubble captured a sequence of images of the comet 73P/Schwassman-Wachmann 3. The comet fragmented, and like 73P, Rosetta’s 67P will likely break some day into two major fragments with debris spreading out as in these images. The Solar wind pressure, as well as any explosive force from the break up, will cause the comet fragments to slowly disperse but effectively remain in the same orbit. (Image Credit: NASA/Hubble)
Stresses due to temperature changes from diurnal variations, the changing Sun angle during perihelion approach, from loss of material, and finally from changes in the tidal forces on a daily basis (12.4043 hours) may lead to changes in the fissure causing it to possibly widen or increase in length. Rosetta will continue escorting the comet and delivering images of the whole surface that will give Rosetta scientists the observations and measurements to determine 67P/Churyumov–Gerasimenko’s condition now and its fate in the longer term.
The fissure is not a very recent event. Universe Today’s Bob King published an earlier image in his blog in September and added a question to illustrate. Whether the crack has widened since that time is not certain. (Image Credit: ESA, Illustration, Bob King)
Stay tuned for a forthcoming article from UT’s writer Bob King about numerous Rosetta mission scientific findings published this week in the journal Science.
Four-image mosaic of 67P/Churyumov-Gerasimenko acquired on Jan. 16, 2015 (ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0)
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!
Position of the Cheops boulder on 67P (ESA/Rosetta/Navcam)
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.)
OSIRIS image of Cheops acquired on Sept. 19, 2014 (ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
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)
Close-up of comet 67P showing the larger of the two lobes (boulder Cheops labelled), jets of dust and likely individual dust particles scattered around the comet. Credit: ESA/Rosetta/NAVCAM
Anyone who’s ever read a Charlie Brown comic strip knows “Pig-Pen”, the lovable boy who walks around in a constant cloud of his own dirt and dust. Every time he sighs, dust rises in a little cloud around him. Why bother to bathe? There’s dignity in debris, which “Pig-Pen refers to as the “dust of countless ages”. Comets shuffle around the Sun surrounded by a similar cloud of grime that’s as old as the Solar System itself.
Dust and gases released by the comet reflect so little light compared to the nucleus they require special processing to see clearly. In this photo, many of the small, irregular specks may be cometary dust grains captured in the 4.3 second exposure. Credit: ESA/Rosetta/NAVCAM
You’ve probably noticed little flecks and streaks in photos returned by the Rosetta spacecraft in the blackness of space surrounding comet 67P/Churyumov-Gerasimenko. After a recent year-end break, the Rosetta team has returned with new updates on the comet including a series of four images recently released as a mosaic. The pictures were processed to highlight surface features; the space around the nucleus is black in comparison. But if we take a closer look at what first appears void, we soon discover it’s not empty at all.
In photos taken January 3rd, the writer of ESA’s Rosetta blog notes that “some of the streaks and specks seen around the nucleus will likely be dust grains ejected from the comet, captured in the 4.3 second exposure time.”
At right is a streak that could either be a larger, fast-moving dust particle that trailed during the exposure or perhaps a cosmic ray hit. Credit: ESA/Rosetta/NAVCAM
Using an image-editing tool like Photoshop, we can hold back the glare of the nucleus and “open up” the shadows around the comet. Jets of dust released by vaporizing ice are the most obvious features to emerge. The soft, low-contrast plumes plow into the vacuum around the nucleus wrapping it in a silky cocoon of gas and dust – a tenuous atmosphere that reflects sunlight far more weakly than the comet itself.
The mosaic image of the comet taken on January 3rd and processed, like most of ESA’s comet images, to highlight surface features. Credit: ESA/Rosetta/NAVCAM
While staring at dust spots may not produce the same magical feelings as watching a sunrise, it’s fascinating nonetheless to contemplate what we’re seeing. If you’ve been struck by the beauty of a comet’s meteor-like head trailing a wispy tail, you’re looking at what countless individual grains of dust can do when sculpted by the master hand of the Sun. Perusing images of 67P, we see the process in its infancy as individual grains and small clots are released into space to be fashioned into something grander.
Image of the first dust grain (center) captured by MIDAS. The bar at top left is 0.01 mm wide. Credit: Courtesy Mark Bentley
Rosetta’s Micro-Imaging Dust Analysis System or MIDAS measures the rate at which dust sweeps past the spacecraft and its size distribution. MIDAS catches dust grains by exposing a sticky target surface into space and waiting for a mote to drift by. It snatched its first one last November – a larger than expected mote measuring about 1/100 of a millimeter across with a complex shape and fluffy texture.
COSIMA’s first dust grains. Left: an image of the target plate (measuring 1 cm by 1 cm) on which the grains were collected; right: a section of the plate showing it on August 17th (top) when no dust grains were visible and 24 August 24th (bottom) when two large dust grains were detected. The plate is illuminated from the right by LEDs, and the length of the shadows is proportional to the height of the dust grains. Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
Analysis of the composition of another dust grain named “Boris” made by the COSIMA instrument has identified sodium and magnesium. Magnesium is no surprise as 95% of known minerals observed in comets resemble olivine and pyroxenes, common in meteorites and in the upper mantle of the Earth. Sodium has also been seen before in comas and tails, and originates in dust grains, but its mineral source remains uncertain.
As we might study the makeup of the dust Pig-Pen leaves in his wake to identify traces of earthly dirt, micro-organisms, pollen, pollution, and even recent volcanic eruptions, so we examine each mote that sprays Rosetta’s way, looking for clues to the origin of the planets and Solar System.
The Cliffs of Churyumov-Gerasimenko: an enhanced and procosessed crop of an image from Rosetta's navcam. Credits: ESA/Rosetta/NAVCAM, processing by Stuart Atkinson.
Images from space don’t get more dramatic than this. Image processing wizard Stuart Atkinson zoomed in on one of the most intriguing views yet of Comet 67P/Churyumov-Gerasimenko, highlighting the contrasts of dark and light, smooth and rugged, soft contours and frighteningly vertical cliffs.
The orginal image, below, is a four-image mosaic made from images snapped by Rosetta’s navigation camera, taken from a distance of 20.1 km from the center of Comet 67P/Churyumov-Gerasimenko on 10 December. The image resolution is 1.71 m/pixel and the individual 1024 x 1024 frames measure 1.75 km across. The mosaic is slightly cropped and measures 2.9 x 2.6 km.
This four-image mosaic comprises images taken from a distance of 20.1 km from the center of Comet 67P/Churyumov-Gerasimenko on December 10, 2014. Credit: ESA/Rosetta/NAVCAM.
A beautiful image of Sasturns tiny moon Daphnis, but where is all the color?
If NASA is so advanced, why are their pictures in black and white?
It’s a question that I’ve heard, in one form or another, for almost as long as I’ve been talking with the public about space. And, to be fair, it’s not a terrible inquiry. After all, the smartphone in my pocket can shoot something like ten high-resolution color images every second. It can automatically stitch them into a panorama, correct their color, and adjust their sharpness. All that for just a few hundred bucks, so why can’t our billion-dollar robots do the same?
The answer, it turns out, brings us to the intersection of science and the laws of nature. Let’s take a peek into what it takes to make a great space image…
Perhaps the one thing that people most underestimate about space exploration is the time it takes to execute a mission. Take Cassini, for example. It arrived at Saturn back in 2004 for a planned four-year mission. The journey to Saturn, however, is about seven years, meaning that the spacecraft launched way back in 1997. And planning for it? Instrument designs were being developed in the mid-1980s! So, when you next see an astonishing image of Titan or the rings here at Universe Today, remember that the camera taking those shots is using technology that’s almost 30 years old. That’s pretty amazing, if you ask me.
But even back in the 1980s, the technology to create color cameras had been developed. Mission designers simply choose not to use it, and they had a couple of great reasons for making that decision.
Perhaps the most practical reason is that color cameras simply don’t collect as much light. Each “pixel” on your smartphone sensor is really made up of four individual detectors: one red, one blue, two green (human eyes are more sensitive to green!). The camera’s software combines the values of those detectors into the final color value for a given pixel. But, what happens when a green photon hits a red detector? Nothing, and therein lies the problem. Color sensors only collect a fraction of the incoming light; the rest is simply lost information. That’s fine here on Earth, where light is more or less spewing everywhere at all times. But, the intensity of light follows one of those pesky inverse-square laws in physics, meaning that doubling your distance from a light source results in it looking only a quarter as bright.
That means that spacecraft orbiting Jupiter, which is about five times farther from the Sun than is the Earth, see only four percent as much light as we do. And Cassini at Saturn sees the Sun as one hundred times fainter than you or I. To make a good, clear image, space cameras need to make use of all the little light available to them, which means making do without those fancy color pixels.
A mosaic of images through different filters on NASA’s Solar Dynamics Observatory. Image credit: NASA/SDO/Goddard Space Flight Center
The darkness of the solar system isn’t the only reason to avoid using a color camera. To the astronomer, light is everything. It’s essentially our only tool for understanding vast tracts of the Universe and so we must treat it carefully and glean from it every possible scrap of information. A red-blue-green color scheme like the one used in most cameras today is a blunt tool, splitting light up into just those three categories. What astronomers want is a scalpel, capable of discerning just how red, green, or blue the light is. But we can’t build a camera that has red, orange, yellow, green, blue, and violet pixels – that would do even worse in low light!
Instead, we use filters to test for light of very particular colors that are of interest scientifically. Some colors are so important that astronomers have given them particular names; H-alpha, for example, is a brilliant hue of red that marks the location of hydrogen throughout the galaxy. By placing an H-alpha filter in front of the camera, we can see exactly where hydrogen is located in the image – useful! With filters, we can really pack in the colors. The Hubble Space Telescope’s Advanced Camera for Surveys, for example, carries with it 38 different filters for a vast array of tasks. But each image taken still looks grayscale, since we only have one bit of color information.
At this point, you’re probably saying to yourself “but, but, I KNOW I have seen color images from Hubble before!” In fact, you’ve probably never seen a grayscale Hubble image, so what’s up? It all comes from what’s called post-processing. Just like a color camera can combine color information from three detectors to make the image look true-to-life, astronomers can take three (or more!) images through different filters and combine them later to make a color picture. There are two main approaches to doing this, known colloquially as “true color” and “false color.”
A “true color” image of the surface of Jupiter’s moon Europa as seen by the Galileo spacecraft. Image credit: NASA/JPL-Caltech/SETI Institute
True color images strive to work just like your smartphone camera. The spacecraft captures images through filters which span the visible spectrum, so that, when combined, the result is similar to what you’d see with your own eyes. The recently released Galileo image of Europa is a gorgeous example of this.
Our eyes would never see the Crab Nebula as this Hubble image shows it. Image credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
False color images aren’t limited by what our human eyes can see. They assign different colors to different features within an image. Take this famous image of the Crab Nebula, for instance. The red in the image traces oxygen atoms that have had electrons stripped away. Blue traces normal oxygen and green indicates sulfur. The result is a gorgeous image, but not one that we could ever hope to see for ourselves.
So, if we can make color images, why don’t we always? Again, the laws of physics step in to spoil the fun. For one, things in space are constantly moving, usually really, really quickly. Perhaps you saw the first color image of comet 67P/Churyumov-Gerasimenko released recently. It’s kind of blurry, isn’t it? That’s because both the Rosetta spacecraft and the comet moved in the time it took to capture the three separate images. When combined, they don’t line up perfectly and the image blurs. Not great!
The first color image of comet 67P/Churyumov-Gerasimenko. Image credit: ESA/Rosetta
But it’s the inverse-square law that is the ultimate challenge here. Radio waves, as a form of light, also rapidly become weaker with distance. When it takes 90 minutes to send back a single HiRISE image from the Mars Reconnaissance Orbiter, every shot counts and spending three on the same target doesn’t always make sense.
Finally, images, even color ones, are only one piece of the space exploration puzzle. Other observations, from measuring the velocity of dust grains to the composition of gases, are no less important to understanding the mysteries of nature. So, next time you see an eye-opening image, don’t mind that it’s in shades of gray. Just imagine everything else that lack of color is letting us learn.
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.
The Philae that could! The lander photographed during its descent by Rosetta. Credit: ESA/Rosetta/MPS for Rosetta Team/
I was twelve years old when Columbia disintegrated. Space exploration was not even a particular interest of mine at the time, but I remember exactly where I was when the news came. My dad and I were sitting in the living room of my childhood home, listening to NPR. I don’t really recall how I felt when they broke into our program with the news, but I remember well the two emotions that seemed to permeate the coverage that soon become constant: confusion and sadness. As I watched the almost surreal saga of ESA’s Philae this week, I found my mind wandering back to that day eleven years ago. That confusion rang out was hardly surprising; after all, things weren’t going right and we didn’t know why. But it was the sadness, I think, that drew my mind into the past. Many of the countless people watching Philae’s distress unfold before us weren’t merely disappointed that a decades-in-the-making experiment wasn’t going as planned. The word heartbroken kept springing to mind.
Let me be unequivocal: the loss of a machine, no matter how valuable or beloved, pales in comparison to the forfeit of human life. The astronauts lost on Columbia, like those snatched from us before and since, left behind families, friends, and a grateful world. But, why, then, did it seem to feel so similar to so many people?
“This is legitimately upsetting” a friend and colleague texted me on Friday as it became clear that the tiny lander’s batteries were beginning to run dry. She was far from alone in her sentiment. Across Twitter, people from around the world seemed to be lashing out against the helplessness of the situation.
Oh, wow. My head knows the mission is successful, and data is safe. My heart…wanted a different ending. #cometlanding
And, in conversations I had with other scientists at the 46th annual Division for Planetary Sciences meeting in Tucson, AZ this week, people seemed almost mournful at the prospect of the lander’s loss. These same researchers had laughed and cheered just days earlier when shown the crater made by NASA’s LADEE spacecraft upon its crash into the lunar surface.
The questions in my mind are numerous. What’s the cause of this inequity? Why do we seem to latch onto certain spacecraft and blithely ignore others? What is it that makes us become emotionally attached to machines in the first place?
In part, I think, our attachment comes from the unprecedented view offered to us by social media. In 1990, an event not so dissimilar from this one beset NASA’s Galileo spacecraft. Flying by the Earth on its way to Jupiter, Galileo had just attempted to unfurl its main antenna, a maneuver critical to the mission’s success. In mission control, they received the bad news: the antenna was stuck. But, the world did not break down in despair. In the days to come, stories would appear in newspapers and on the nightly news, but a world where even email was in its infancy lacked a means for the average citizen to follow along with every detail.
Nineteen years later, this would not be the case. As soon as it became clear to those in ESA headquarters that something had gone very wrong during Philae’s descent, we all knew. And, as data began to trickle in about one bounce off the surface and then another, we all cringed. When the last power drained from the lander’s batteries, we followed along, one volt after another. Philae may have been the pride of the ESA scientists and engineers who designed it, but it felt like it was ours.
But, it didn’t feel like ours in the way that a car or a plane or even a space station does. It felt like our friend. No doubt, this can be directly linked to the first person point of view employed for its Twitter account. Instead of the @Phillae2014 account reporting “the Ptolemy instrument has made a measurement,” we get “I just completed a @Philae_Ptolemy measurement!!” It seems like a small change, but it opens up a whole new world of connection with this distant traveler. At no time was this clearer than when things started to go wrong.
Hello! An update on life on #67P – Yesterday was exhausting! I actually performed 3 landings,15:33, 17:26 & 17:33 UTC. Stay tuned for more
How poignant is that? Two travelers talking to one another from across the solar system. But, as Philae’s time began to wind down, the messages tugged even more urgently on our heartstrings.
And, it all pales in comparison to the way China’s Yutu rover signed off when it looked like a malfunction might cause it to freeze to death on the Moon (original Chinese, CNN translation):
… my masters discovered something abnormal with my mechanical control system. …I’m aware that I might not survive this lunar night…
The sun has fallen, and the temperature is dropping so quickly… to tell you all a secret, I don’t feel that sad. I was just in my own adventure story – and like every hero, I encountered a small problem.
Goodnight, Earth. Goodnight, humanity.
Talk about heartbreaking.
This personal point of view combines particularly effectively with landers and rovers. These craft seem more human than ships like Cassini or Galileo, with their silent glide through deep space. When something goes wrong with a surface explorer, as it did with Philae or Yutu, it plays on our deepest fears. Every time we’re lost, the little voice of panic begins to creep into our thoughts: “what if this is the time that I can’t get back?” Reading the “thoughts” of a tiny spacecraft, lost and alone and confused, puts us right there ourselves. As mission controllers edged towards desperation in their attempts to save the stricken explorer, we knew how that delirious urgency felt. Our attachment becomes almost unavoidable.
So, what does this all mean? I think it’s a clear signal that people are engaged by the exploration of space. When it comes to us in the right way, on our terms, it’s a big hit. By anthropomorphizing these robots, we humanize the science that they do. Suddenly a machine more than 500 million kilometers away becomes more relatable than the scientists next door who control it. Perhaps ESA, NASA, and other space agencies can extend this relationship even further. Rather than springing to “life” upon liftoff, spacecraft can share with us their view of the entire process, starting not from space, but from the first drawings on an engineer’s blackboard.
One thing’s for sure, though. A relationship like that won’t make times like these any easier to handle.
