2009

Dr. Drake Deming, Senior Scientist, Solar System Exploration Division, Goddard Space Flight Center

Deming: Yes. That’s the same as EPOCh. EPOXI is a combination of EPOCh and DIXI (Deep Impact eXtended Investigation). DIXI is the component of EPOXI that goes to Comet Hartley 2, and that’s now ramping up because EPOCh is finished.

NTB: What is that mission designed to accomplish?

Deming: Well, I’m not involved in that, but it’s designed to image a comet nucleus. It will use the imaging capability of the Deep Impact flyby spacecraft to image another comet. The original Deep Impact mission released an impactor into a comet nucleus and actually blew a crater in it. Of course, the impactor is no longer available to us because it was used up, but still, a tremendous amount can be learned by imaging another comet nucleus for comparative purposes.

NTB: That was the Temple 1 comet, right?

Deming: That was the Temple 1 comet.

NTB: EPOXI spent most of the month of May observing a red dwarf star called GJ436 that is located just 32 light years from Earth, and it has a Neptune-size planet orbiting it. What did you learn from those observations?

Deming: We’re still very intensely analyzing those data, but what we hope to learn is whether there’s another planet in the system, and in this case our sensitivity extends down to Earth-sized planets, so we’re looking for another planet that may have left a small signature in the data as it transited the star. If we can find that, there’s a good chance that that planet might even be habitable. Because our period of observation extends for more than 20 days, and because this is a low-luminosity red dwarf star, the habitable zone in that system is in close to the star where the orbital periods are on the order of 20 days. So we have sensitivity to planets in the habitable zone in this case.

Of course, those data have our highest priority and we’re inspecting them very intensely. However, the data analysis process is very involved. We have a lot of sources of spacecraft noise that we have to discriminate against.

NTB: In July 2008, NASA’s Deep Impact spacecraft made a video of the Moon transiting – or passing in front of – the Earth from 31 million miles away. Why did that video generate so much excitement within the scientific community?

Deming: Well, I think it generated a lot of excitement both in the scientific community and outside of the scientific community because it’s really, I think, the first time that we’ve seen the Earth/Moon system from that particular perspective, from that specific perspective, where you see the Moon transit in front of the Earth. And there’s also, as we analyze those data, some realization that although it would be a relatively low probability that, if that were to occur for a planet orbiting another star and its moon transited in front of it, we could learn about the topography of the planet.

NTB: Do you think we’ll learn anything new about Earth from that video?

Deming: I think we’ll learn new things about the Earth as a global object, as an astronomical object. For example, one of the things we should start prominently seeing in the data is the sun glint from the Earth’s oceans, and this has been hypothesized as a way to detect oceans on planets orbiting other stars because that glint would be polarized. Although we don’t have any polarization capability, we can see that the glint sometimes becomes dramatically brighter and we’re trying to understand why that is. It may be because the glint is a specular reflection, probably from the Earth’s oceans, so by correlating that glint, the brightening of that glint with, for example, winds across the oceans and wave heights, we may find that smooth patches of ocean give us a particularly strong glint. So, if the glint were observed on an extrasolar planet, we could then infer from a variable polarization signal the presence of the glint and the presence of oceans.

NTB: It was discovered some time ago that Deep Impact’s high-resolution camera has a flaw in it that prevents it from focusing properly. This was a problem during its original mission when it was trying to study a crater made by an impactor on the comet Temple 1, but you were somehow able to use that to your advantage to study planets passing in front of their parent stars. Can you explain how that works?

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