Emily LakdawallaJul 01, 2005

Deep Impact encounter minus 3 days

OK, I'm in...I arrived at an unusually empty Jet Propulsion Laboratory this morning in advance of the first Deep Impact encounter press conference. (It's empty because most JPL employees have Friday and Monday off for Independence Day Weekend -- no such luck for me or the Deep Impact team.) I've gotten my Enormous Bright Orange Badge identifying me as MEDIA and I seem to have pretty good wireless Internet access, so I am ready to write and tell you everything I find out about what's going on with this mission.

Just to set things up: Deep Impact is about to split into two pieces, sending one on a collision course for comet Tempel 1. The mission is designed to expose fresh materials from the interior of a comet to human eyes for the first time. Not only will Deep Impact be watching, but so will a dozen spacecraft and more than a hundred telescopes (many hundreds if you count all the amateurs who are making real contributions to the impact observations).

The impact is scheduled to take place at 22:52 Pacific time on Sunday July 3 (05:52 July 4, UTC), plus or minus three minutes. (Here's the complete timeline.) This morning's press conference is the first for the weekend. Then there is a quiet period, on Saturday -- which is when I'll take my holiday weekend, thank you very much! -- and then things get busy on Sunday, beginning with a press conference at 11:00 Pacific time. Then, at 8:30 in the evening, NASA TV coverage begins continuously, through the impact, and finally they plan a press conference at 1:00 in the morning on July 4 (08:00 UT). I'll be here at JPL through all those events, letting you know what's going on with the mission as I get the news.

Everybody cross your fingers that Deep Impact hits the target and we see a spectacular impact event!

Before the press conference started I had a quick chat with Peter Schultz, the Brown University impact scientist on the mission, and a former professor of mine. I asked him if there was anything that he's done that has compared with the size of Deep Impact. The biggest "boom" he's made involved a 7-kilometer-per-second projectile, only about 2/3 as fast as the Deep Impact collision will be. And the biggest crater he's made experimentally is about a meter across. He commented that he's probably made a bigger splash belly flopping into a swimming pool!

A second conference, and second panel, of scientists instead of engineers this time. The conference hasn't started yet but there is already humor. Mike A'Hearn, the Principal Investigator (PI), is in the middle of the panel and they've just powdered his balding dome as he laughed with embarassment. A scientist in the audience behind me joked "they don't like specular reflection!" You know you're a geek when you laugh at stuff like that. (I'm sad to report that I did laugh.)

Who smiled this time? Nobody. They all sort of smirked. I sure wish people would smile when they are introduced on these press panels! However, it was a pretty punchy group. Don Yeomans especially was cracking all kinds of silly jokes throughout the conference.

Tom Morgan, Program Scientist from NASA HQ (the only one wearing a jacket and tie): "5 billion years is a long time," he joked, as it took a while to get the video up showing the formation of the solar system, which he showed in order to explain why comets are important -- because they represent a "small remnant" of the Icy Parent Bodies that formed the ingredients for the solar system formation.

Don Yeomans, Co-Investigator, from JPL: makes the point that the comets that we see in the middle of the solar system are "middle aged" because of the experience they have had in the inner solar system, losing their volatiles. He keeps calling it the comet "nu-cyoo-lus." He emphasizes the resolution we'll get from Deep Impact. Giotto best resolution on Halley was 100 meters, "the length of a football field." ... "In planetary science, better resolution is better." Deep Space 1 best resoluion at comet Borelly was 50 meters, "half a football field." More recently, Stardust best resoluion on Wild 2 was 25 meters, "a quarter of a football field. Our mission is going to resolve objects on the surface about the size of the football, a huge leap forward in resolution."

Mike A'Hearn, Principal Investigator (PI), University of Maryland: "Where are we now? We are still very far from the comet, but we're closing very rapidly. We're already getting very good science results out of the mission. This is one of the very few occasions where we've had continuous viewing of a comet, and we can begin to understand what drives these. They are very short, not much stuff comes out, and they dissipate very quickly. Sneezes. The coma expands very rapidly over half a day. It dissipates rapidly enough that there is no issue for spacecraft hazard at all," which probably isn't quite true overall. I think maybe he meant that yesterday's outburst is of no concern to the spacecraft. A'Hearn emphasized that the Dan Maas video is an artist's conception, "one of many possible scenarios." ... "The events will unfold over days, so we need a worldwide distribution of observers."

Jessica Sunshine, Co-Investigator, from Science Applications International Corp (SAIC), is a spectroscopist (and another former Brown student). "We have almost a thousand different colors of light that we are going to be looking at," in the infrared. Rosetta will be looking in the ultraviolet. Jessica had the bravery to show "squiggly lines," a spectrum of the comet; press officers don't usually like showing spectra because they think the public won't understand them. Jessica is a really good explainer -- I'll get her spectrum and show it to you in a later note.

Jessica continued, rhapsodizing about the spectra she showed: "It was exciting to see anything, 10 days before the encounter. We can identify water, complex hydrocarbons, CO and CO2, and what is refreshing, we can compare to what we have seen previously from the VEGA mission to Halley, and we are seeing almost the same kinds of materials -- but we were 300 times farther away from Tempel 1 than when VEGA was at Halley. We are getting signals 50 times brighter now than even what you see here. From looking at data, we were able to tell that water in the outburst was double what it had been prior to the outburst."

Jessica said that Deep Impact will see unique stuff. "From telescopes, we mostly see the outer coma or atmosphere. But the materials that come out of the comet are short-lived. They react with each other and with solar radiation to make secondary materials, and that's what we see from far away. But with Deep Impact we will be able to see the primary materials as they come out. We are trying to see materials that are on the inside. Like any good geologist, we take our hammer and we hit it, to see how hard it is and see what's inside. These materials have not seen the light of day for 4.6 billion years. That is what we're waiting to see. These materials are going to pass in front of the spectrometer and we are going to see the compositional variation on the inside of the comet." A crater has inverted stratigraphy, so that "the materials that were deeper are now on top. I'm fond of our impactor, our geologic hammer."

Pete Schultz, Co-Investigator, Brown University. "My students call me the 'Master Blaster.'" [They called him lots of other things too, but I won't repeat those here.] "We know how big it is, but we don't know the nature of the comet. Our strategy is to explore the various options -- not just to look at the crater at the end, but to study the materials as they come out, all the way to the initial flash." He shows pictures of the NASA Ames Vertical Gun Range, which is a really, really, really cool experimental device. I envy Pete's students the chance to create impacts at many kilometers per second in a vacuum chamber. "Every time I do one of these experiments, I am surprised. I think that is the best-case scenario -- that we will be surprised."

Now it's time for press questions.

Dave Perlman asked whether the spectrometer could detect rock as well as ice composition. Jessica answered: "Our spectrometer was specifically designed both for the coma and the geology, both for ices and tars, and for silicates, the rock-forming minerals. It's going to be quite a challenge to unravel it all, but if it's there, we're going to see it."

Someone asked if they know what causes the outbursts. A'Hearn: Ideas for outbursts "include the ideas that they come from impacts, transitions from amorphous ice into crystalline ice, and a variety of other things. By looking at the changes in chemical composition in a natural outburst, I think we will be able to pin down the many mechanisms responsible." He emphasized again the benefits of the intensive observing plan, which is unusual for a comet. Latest outburst was yesterday morning, not today as Grammier had said earlier, A'Hearn clarified.

Are we seeing unusual activity at Tempel 1 since it's close to its perihelion (closest approach to the sun)? A'Hearn: "The overall activity of Tempel 1 had been observed at previous perihelion passages. The overall activity peaks a few months prior to perihelion, so the overall activity is decreasing. So it's basically a seasonal effect -- it's summertime where the active part of the comet is. Some comets are active before, some after perihelion. In detail, each one is different. The biggest outburst doubled the amount of water in the coma -- but we haven't worked out the numbers yet."

Someone asked Jessica what the minimal success criteria were: "We certainly want to hit the comet and watch what happens, and as Pete said, we hope to see some surprises."

Will Deep Impact help in defending Earth against cometary impactors? A'Hearn: "It sure is easier to change the course of something if you know what it is that you are changing the course of. You cannot design a sensible defense system if you do not know what the impactors are."

I'll be writing these two press conferences up into a more formal news story, which I'll post later today.

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