Season's Greetings From Rosetta and Philae!

I had planned to publish this article tomorrow. Alas, @ESA_Rosetta tweeted an adorable Rosetta / Philae Christmas cartoon today that convinced me this article should have a December 25 publication date:

Merry Christmas from #67P, 527 million km from Earth! pic.twitter.com/NhUJAzi7Aq
— ESA Rosetta Mission (@ESA_Rosetta) December 25, 2014

The European Space Agency's Rosetta mission to comet Churyumov-Gerasimenko (aka 67P) launched in 2004 and arrived at its destination earlier this year. One of the mission's first surprise findings came when Comet 67P - assumed to be potato-shaped - resolved to look more like a... rubber duck! Comet 67P is two-lobed, with one lobe distinctly smaller, giving it a familiar shape in human terms. Certainly, "the rubber duck comet" is a less challenging name to pronounce than "comet Churyumov-Gerasimenko!

On November 12, 2014, the Philae lander detached from the Rosetta spacecraft to perform the first comet landing in history. The maneuver was far from perfect - Philae's harpoons meant to anchor it to the comet surface did not fire, nor could the screws in Philae's feet deploy to secure the probe to the comet. As the lander touched down, it actually bounced back into space - not once, but twice, before landing on its side. Regardless, for the first time ever, human eyes are able to get a close-up look at an ancient celestial object in our solar system! 
 

Photo credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Above is a full color image of Comet 67P/Churyumov-Gerasimenko that Rosetta took last August through red, blue and green filters. This is how the comet would appear to human eyes, revealing that it is... gray. When this picture was taken, Rosetta was about 120 km (75 mi) distant from Comet 67P, before Philae was deployed. The comet's uniformly gray appearance suggests that any water ice it contains is distributed more or less evenly throughout the comet's two lobes. If there were alternate patches of all-water ice or all-rock we would expect some areas of the comet surface to be brighter than others. The black areas are shadows caused by sunlight streaming across a surface full of steep cliffs and boulders.

Photo credit: ESA/Rosetta/NAVCAM

Most recent image of Comet 67P taken December 16 by Rosetta, orbiting the comet, with Philae on the surface.

Photo credit: ESA/Rosetta/Philae/CNES/FD 

Simulation of Philae on the surface of Comet 67P - Philae is wedged sideways between the base of a cliff and a large rock outcropping, with one of its legs stuck between rocks. After its initial comet touchdown, Philae bounced twice before coming to rest in its current position. Philae was meant to fire harpoons upon landing to anchor itself to the comet and deploy screws in its feet to secure itself in place during its trip around the sun.

Photo credit: ESA/Rosetta

These are Philae's 10 science instruments. It is currently unknown to which extent some or all of them can be used during the primary science mission. Philae is now in hibernation mode, as it is stuck in an area of the comet surface that gets only a few hours of sunlight per day - not enough to wake the probe from hibernation. This may change as the comet approaches the sun in coming months. If Philae can be roused from its deep sleep, we may yet obtain a treasure trove of data about what happens when comet 67P approaches perihelion.

For now, let's keep in mind that Philae has been functioning at only a fraction of its intended capacity and yet was already able to return an incredible set of never-before-seen comet data.

Photo credit: ESA/Rosetta/Philae/CIVA 

Philae's very first picture is a bit of a blur since the lander was bouncing at the time.

Photo credit: ESA/Rosetta/Philae/CIVA 

Comet close-up: Photo of the cliff right in front of Philae that is blocking its sunlight. The image reveals a number of fissures and fractures. The reflective glare on the rock is caused by the lander.

Credit: Rosetta/ESA

In addition to data that Philae may yet collect on the comet surface, the Rosetta spacecraft continues to accompany 67P and Philae as they journey towards the inner solar system. Rosetta will orbit the two-lobed comet at altitudes of as little as 6.5 km (4 mi). Already Rosetta has returned spectacular images such as the above - cometary cliff faces that are more than half a mile high (ca.1 km). The whole comet is about 4.5 km (2.8 mi) wide, measured duck head to duck tail.

Comet ISON ~ The Perils of Sungrazing

Sadly, Comet ISON did not survive its close encounter with the sun on Thanksgiving Day. At the same time, following its journey live on twitter via existing instruments deployed to observe the sun was a roller coaster ride of celestial excitement. As it approached the sun, ISON brightened, then faded, as would be expected if the sun's heat and intense tidal forces destroyed the nucleus.

The Solar Dynamics Observatory (SDO) did not capture ISON at all at perihelion. The Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO) imaged ISON as a bright nuclues trailing a long coma and a smaller, narrower dust streamer, as it plunged towards the sun. Both SOHO and STEREO, which are not optimized for comet viewing, did not capture ISON during its closest approach to the sun. Once enough time had elapsed for ISON - if it survived - to have rounded the sun and reappear in SOHO images, there was no trace of the comet. Astronomers and the twittersphere reported on Comet ISON's fiery demise, some with sadness, some with humor, as evidenced in twitter comments such as the sun having roast comet for Thanksgiving.

Then, almost 24 hours post-perihelion, it became evident that *something* had rounded the sun, as ISON - or what was left of it - once again appeared in SOHO images. ISON looked much dimmer, more diffuse and with only the faintest of tails, indicating the nucleus had most likely broken up. As the cometary remains sped away from the sun, ISON's brightness faded. Comet ISON was no more - even as it left scientists with a treasure trove of cometary data that will advance our knowledge for years to come.

Below is an animation of SOHO images showing ISON's ill-fated encounter with the sun:

Perhaps ISON has a little different view on all of this:

Image credit: http://xkcd.com/1297/

See previous post below for a collection of beautiful images taken around the world as ISON passed closed to Earth on its way to perihelion in November.

Comet ISON - Celestial Display Of Our Lifetime?

Update - November 9, 2013:

Comet ISON continues its journey to the center of our solar system for its perilous Thanksgiving Day maneuver around the sun. Whether or not ISON will survive its close encounter with our sun is still unknown. 

Astronomers will keep a close eye on ISON and study the comet's composition by observing which gases boil off the comet's core as it approaches perihelion. 

At the time the image below was taken, ISON was 212 million km (132 million mi) from Earth, roughly half the distance to Mars. 

The picture was taken on October 25, 2013 with a 36-cm (14-in.) telescope at Marshall Space Flight Center in Huntsville. I have not yet come across ISON sightings with the naked eye. Please let me know if you have sightings or photos to share in this post as I publish updates during ISON's approach.

The streak across the right side of the photo was caused by the passage of Italy's SkyMed2 satellite through the frame.
(Thanks for the photobomb, SkyMed2!)


 

 Image credit: NASA Marshall Space Flight Center

Comet ISON on its way to the sun - October 25, 2013

Image credit: Adam Block via spaceweather.com

Comet ISON - October 8, 2013

The above image was published on the website for the Comet ISON Observing Campaign (CIOC), along with an article that explains why ISON appears to have a greenish tinge.



 

Update - November 6, 2013: 
As we close in on Thanksgiving Day and ISON's hairpin turn around the sun, the comet's fate at perihelion is still unknown. Amazing images have emerged of ISON's journey into the inner solar system. Astronomers on Earth have already imaged it. 





We are only four months away from what could turn out to be the most stunning astronomical event of the year - potentially of our lifetimes and the entire century. Or we could end up disappointed. 

It all depends on whether or not Comet ISON will survive its plunge towards and tight turn around the sun during the far end of the outbound leg of its orbit. The comet is known as a sungrazer because of how closely it will travel to the sun. Space.com has a nice infographic that illustrates ISON’s journey through our solar system.

ISON was discovered only recently, in September 2012, by Russian astronomers Vitali Nevski and Artyom Novichonok. The comet is named after the telescope for the International Scientific Optical Network (ISON), which is operated by an association of 10 nations that cooperate to track objects in space. 

This image of ISON on its way to Earth was taken by the Hubble Telescope on April 30, when ISON was traveling between Jupiter and the asteroid belt on its way to the inner solar system. The image is a composite of five photos taken by the Hubble’s Wide Field Camera 2 UVIS instrument. Three exposures were taken with a filter that let in yellow and green light (seen as blue in the image) while two used a filter that let in red / infra-red light. The result is a simulation of what human eyes would see if they looked at ISON with the Hubble telescope’s resolution.

Image Credit: NASA, ESA, Hubble Heritage Team

This breathtaking image of Comet ISON heading towards Earth and the Sun was taken by the 

Hubble Telescope on April 30, 2013

To give you an idea of what you are truly looking at, consider the following:

- Comet ISON originated in the far regions of our solar system in the Oort Cloud and started its journey 10,000 years ago.

- This is thought to be ISON’s first trip into the center of our solar system. But if it isn’t, humanity would be unlikely to have a record of a prior passage.

- ISON will travel within 724,000 miles (1.16 million kilometers) of the sun’s surface at its closest approach, while making a hairpin turn around the sun. 

- The comet’s nucleus is 3-4 miles wide and consists of ice, gas and dust particles. The comet’s tail is created as ISON heats up plunging toward the sun, trailing a tail of particles that will grow by 200 million kilograms per day as dust and ice evaporate off the nucleus. 

- ISON’s tail is already gigantic – long enough to wrap around the Earth seven times.

- If ISON survives its brush with the sun’s heat, radiation and tidal forces on Thanksgiving Day 2013, it will light up the skies for days, even weeks, and appear as bright or brighter than the moon this December. 

- ISON’s celestial display could well equal breathtaking displays of previous comet sightings in history.


If ISON delivers upon its promise of a jaw-dropping celestial display, I will throw a comet watching party in December for my birthday. 

Reading about ISON reminded me of Gregory Benford’s and David Brin’s visionary book Heart of the Comet (1986). What if we could hitch a ride on ISON at its closest passage to Earth, establish a colony inside the comet’s nucleus and send “cometary humans” off onto a journey to the furthest reaches of our solar system – a voyage that will not return back to Earth for many thousands of years?


To me, ISON’s discovery only last year, its close passage to Earth, along with the recent surprise meteor impact in Russia represent another wake-up call that we must redouble our efforts to make human life multi-planetary. What if ISON were headed for a collision course straight with Earth? Would we be able to muster the technology, capacity and international cooperation needed to prevent impact in a few short months? What if we couldn’t? Our planet would survive but would humanity be as lucky? How big will the next asteroid be that we can’t see coming because it well be headed for Earth straight out of the sun like the Russian meteorite? What if the next one is ISON-sized? Can we as a species really afford to sit on our hands and do nothing while we have the technology to colonize the moon and Mars?



Update - July 29, 2013: 
Well, it was fun to imagine cometary fireworks in our skies for a couple hours.... Here is an interpretation of available observation data that predicts ISON will likely break apart before perihelion or will not survive its close encounter with the sun.