A photo of Comet 67P/Churyumov-Gerasimenko taken from the Rosetta orbiter.

Note: I am writing this almost two years after the fact. Life has been busy and events carry one onward, but for the next week I hope to do some catching up on this blog. Fortunately, I took good notes and can remember most of what we did at the American Astronomical Society conference in Seattle in January, 2015.

Dr. Paul Weissman, a scientist at JPL (now at the Planetary Science Institute) who worked the Rosetta mission.

On the second full day of the AAS conference in Seattle (Jan. 6, 2015), we had an incredibly busy and fulfilling day. This was the main day for educational posters and presentations, so I divided my time between a plenary session and presenting two posters. One I created on my own from my astronomy lesson plans that came out of my Research Experiences for Teachers (RET) program at Brigham Young University. The other one was a group poster created by the four educators involved in the NASA/IPAC Teacher Archive Research Program (NITARP) under Dr. Louisa Rebull.

An artist’s illustration of the Rosetta orbiter and Philae lander. The comet wound up being much more interesting that this illustration shows.

Before the beginning session, I called my students and none of them wanted to go with me to breakfast (they wanted the extra sleep), so I walked to a small convenience store nearby and bought some donuts and juice, which I ate back at the hotel room. I then walked to the convention center.

Plenary sessions are scheduled so that nothing else is going on and everyone can attend. The opening plenary session this day was by Paul Weissman, a scientist at JPL for the Rosetta-Philae mission to comet 67P/Churyumov-Gerasimenko. The European Space Agency built Rosetta, but management and data analysis tasks were shared between several agencies including JPL at NASA.

The large auditorium was full, and I sat toward the front to better see the slides. He had previously worked on the Galileo and Stardust missions. He worked on the Champollion lander/sample return mission, which was eventually scrapped, but much of the work and design was used in the more advanced Rosetta/Philae mission. It launched in March 2004 on an Arianne rocket and took a slow looping ride and several gravity assists (three of Earth and one of Mars) to catch up to the comet, arriving in July 2014 after encountering two asteroids.

Another view of the “rubber ducky” shape of comet 67P/Churyumov-Gerasimenko, taken from the Rosetta orbiter.

The Rosetta orbiter had 12 instruments and the Philae lander had nine. It was sent down very slowly toward the comet on Nov. 12, 2014 and was supposed to fire two harpoons that would stick it to the surface. The comet is small and lightweight compared to asteroids, so there isn’t much gravity and the idea was to prevent the lander from bouncing off. They picked a landing site that was the least objectionable to the scientists and had safe terrain.

Diagram of the Philae lander. The MUPUS are two harpoons that were supposed to anchor the lander to the surface of the comet, but the lander bounced off and came to rest wedged on its side next to a cliff.

Unfortunately, the harpoons failed and the lander did bounce off. It took a slow arc up and eventually landed in the worst possible place, wedged up in a corner on its side next to a small cliff where sunlight can’t reach it very often. The lander had batteries for only about two days, and wasn’t able to use some of its instruments because of its awkward position. Yet it did return useful data while its batteries lasted and is considered a success.

An analysis of the images from the Rosetta orbiter show three holes where the lander feet tried to touch down – the two harpoons didn’t fire, possibly because the surface was softer than expected. Apparently the friable surface ice overlaid a much harder layer, which no one suspected was there. The resulting force of the landing poked the holes through the outer surface, but it hit the harder layer, rebounded, and launched the lander back into space.

Final resting place of the Philae lander after it bounced off the surface of Comet 67P/Churyumov-Gerasimenko.

Every comet we’ve visited is unique. Some are fairly active, such as Halley or Wild 2. Others are older and aren’t outgassing much because their surfaces are covered with dark gunk – mostly carbon with a surface albedo of less than 5%. That makes them very hard to see – about the color of black printer toner powder. Comet 67P/Churyumov-Gerasimenko is one of these dark comets, covered with old outgassing basins. It looks as if two smaller comets collided and stuck together, with a thin neck between the two larger lobes that make it look something like a giant rubber ducky.

Dr. Weissman spoke of some of what we’ve learned from Rosetta-Philae. The comet rotates just over once per 12 hours (there is some variability due to outgasing) and is about 4 km in diameter. The dark outside layer insulates the remaining ice, and the neck area acts as a heat sink. The unusual shape creates stresses inside which can be seen as cracks in the surface. Analysis of its density (mass to size) and radio sounding of its interior show that it is made of some rubble (smaller boulders) and mostly dust. It contains more silicates and organic compounds than ices. It has a halo of smaller particles the size of hailstones orbiting around it. Its water ice has a different isotope ratio, with more deuterium than Earth water, which means Earth did not get its water from comets like 67P. It apparently formed in the very early solar system even before the Sun’s accretion disk was fully formed.

They have hopes that when the comet gets further in its orbit later in the year, sunlight might reach the lander and they will try to re-activate it. As of this writing (December 2016) they were able to successfully regain sporadic communication with the lander in June and July of 2015. At the end of the mission, the Rosetta orbiter was slowed down to gradually move in toward the surface and land as softly as possible on September 30, 2016.

My personal poster at the AAS education poster session on Tuesday, Jan. 6, 2015. It explains several lesson plans I taught in my astronomy class that were developed from my work at the BYU-RET during the summer of 2014.

I had dropped off my poster prior to the plenary session, so I hurried from the session to the poster exhibit hall and tacking it up, then laid out copies of the lesson plans it describes. I’d had the poster printed at Kinko’s a few days before leaving for Seattle and carried it with me on the plane. For most of the remainder of the day, I attended to the poster and explained things to visitors. I had a good stream of people stop by, many of which were astronomy educators. Some were even from PhD programs in Science Education that I might someday apply to.

The lesson plans I presented included (1) using Adobe Photoshop to take WISE images from three wavelengths and combine them into the RGB channels as a representative color image, (2) charting Spectral Energy Distributions using data from SIMBAD and IPAC, and (3) calculating star distances using the distance-modulus formula. I’ve written up blog posts previously on each of these lessons, so you can scroll down to my other blog posts to find them.

Dr. Eric Hintz of Brigham Young University presenting his poster at the AAS educational session.

Dr. Eric Hintz, my mentor for the RET program at BYU, had his own poster near mine on using virtual reality glasses (Google Glass) to provide translation services in ASL for deaf visitors to the BYU planetarium. Before, when deaf people visited and ASL services were used, the planetarium couldn’t be darkened all the way so that the translator could be seen. Now, the translator can be in another room and videotaped, then projected into Google Glasses for the deaf visitors.

Chelin Johnson (left with camera) and her students presenting their poster on an independent project at the AAS education poster session.

Chelin Johnson and her students had their own educational poster a few spaces down from mine. She has been a SOFIA Airborne Astronomy Ambassador like me, participated in NITARP, and has her students do independent WISE projects each year, which they present at this conference. It is a great example to me of what’s possible.

John Gibb, Elin Deeb, Estefania Larson, and David Black presenting their poster on the NITARP education program at the AAS conference in Seattle; Jan. 6, 2015.

We had divided up the times during the day for who would stay with our group NITARP educational poster, so I spent some time with it in the afternoon while also trying to see the other posters in the section. I was so busy all day trying to stay at two posters that I didn’t take time for lunch. When the day ended at 6:00, I was very ready for food. The EPO people at the SOFIA booth had arranged for a dinner at The Cheesecake Factory, and my students were invited. Elena and Kendall had other plans, but Rosie and Julie came with me. It was a good meal (I’d never eaten here before and hadn’t realized they have complete meals and not just cheesecake).

David Black standing by his poster at the AAS education session; Jan. 6, 2015.

We had quite a group, and Ryan Lau was there (he was presenting a poster at the conference) and I asked him to explain his research to my students. He has now completed his PhD program at Cornell and explained what he’s been working on for his thesis. I wish I had brought along my cameras and could have recorded what he said. I had dropped them off in my room before supper, and didn’t have my notebook with me, either. My students were impressed and both became more interested in pursuing a career in astrophysics, hearing how Ryan’s work was so accessible. He talked about SOFIA’s instruments, how he has studied the galactic core and its accretion ring, and some of the huge Luminous Blue Variable stars near it.

Presenting my poster at the AAS conference.

I was pretty exhausted after the dinner. I tried to get some work done back at my hotel room, but soon had to crash. It had been a great day of meeting people and sharing my astronomy lessons.