May 22, 2006
Part I: Astrobiology
Planets Around Other Stars
Heidi Hammel,
Space Science Institute
43 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)
"Do there exist many worlds, or is there but a single world? This is one of the most
noble and exalted questions in the study of Nature."
Albertus Magnus (1193–1280)
In all previous lectures, as well as for the vast majority of those to come, the lectures have been those of one scientist speaking to a room filled with other scientists, recorded live at a conference.
This lecture is different. It was a public lecture given just a month ago to middle school children, sponsored by the National Science Foundation's ADVANCE program, a program specificially designed to enthuse and excite young girls into considering careers in mathematics, science and engineering.
Science is at once several substantially different activities. At one level, it is the highly disciplined organization and verification of what we believe we know. On another, it is the joyous exploration of the unknown. And at a third level, it is the preparation of the next generation to continue the search.
We are now embarking on a new series of Voyages of Discovery, reminiscent of Magellan, Cook and Darwin, but at a speed unparalleled in prior history. For this talk, Hammel created her slides in March 2006. At that time, there were 155 planets known to exist outside our solar system. By the time that she gave the talk in mid-April, that number had grown to 163. Now, at the time of this writing in mid-May, the number is 170. We are discovering new planets at a rate of three to six a month now.
But we've just begun. It's been estimated that contained within the 10 parsec (32.6 ly) sphere surrounding Earth that there should be 30,000 planets. Some of these planets will almost certainly harbor life, and their discovery will transform evolutionary biology — if for no other reason than we are certain to be surprised.
And we already have been. As Hammel discusses in the lecture, prior to 1995, we had no evidence of any planets outside of our own solar system. Because we were limited to just this one instance, we attempted to extract every bit of information we could from its existence. The resulting story we told ourselves was both intricate and convincing: planets that formed near the central star were terrestrial in nature (Mercury, Venus, Earth and Mars), stony iron planets that had had their gaseous volatiles scrubbed clean by a constant solar wind. Only when the planets formed further out would they be allowed to become gas giants (Jupiter, Saturn, Uranus and Neptune).
But the first extrasolar planets discovered were far from Earth-like. They were "hot Jupiters," orbiting just off the surface of their suns in 4 day years, something we did not even believe was possible. Indeed, we still don't believe that these planets could have formed where they are. Current thought has these planets migrating inward in billion year trips.
The method by which these planets were discovered heavily biased the initial discoveries to finding these close-in Jupiters. We watched the light emanating from the central star being shifted from blue to red and back again in a periodic motion as these unseen massive planets jerked their suns around with each orbit, but this "radial velocity" method is far too insensitive to detect Earth-sized planets, especially at orbital distances similar to the Earth's. The planets we've discovered to date are by necessity large.
To correct that deficiency, we are now in the process of building a number of spacecraft designed to be able to detect Earth-like planets. One of these missions is the Terrestrial Planet Finder. The TPF is composed of two complementary observatories, an optical wavelength coronagraph and an infrared interferometer, to be launched perhaps in 2020. Heidi is a member of the TPF coronagraph mission, and she speaks to its promise near the end of her talk.
— Wirt Atmar
About the Speaker
Heidi B. Hammel is a Senior Research Scientist with the Space Science Institute in Boulder, Colorado, and is Co-Director of Research at the Institute, although Hammel herself lives and works in Ridgefield, Connecticut.
She received her undergraduate degree from the Massachusetts Institute of Technology in 1982 and her Ph.D. in physics and astronomy from the University of Hawaii in 1988. After a post-doctoral position at the Jet Propulsion Laboratory (Pasadena, California), Hammel returned to MIT, where she spent nearly nine years as a Principal Research Scientist in the Department of Earth, Atmospheric, and Planetary Sciences.
Hammel primarily studies outer planets and their satellites, with a focus on observational techniques. For the impact of Comet Shoemaker-Levy 9 with Jupiter in July 1994, Hammel led the Hubble Space Telescope Team that investigated Jupiter's atmospheric response to the collisions. An expert on the planet Neptune, she was a member of the Imaging Science Team for the Voyager 2 encounter with the gas giant in 1989. Her latest research involves studies of Neptune and Uranus with Hubble and other Earth-based observatories. Hammel is also an Interdisciplinary Scientist for Hubble's successor, the James Webb Space Telescope, which is scheduled for launch in 2011.
Dr. Hammel received the 2002 American Astronomical Society's Division for Planetary Sciences (AAS/DPS) Sagan Medal for outstanding communication by an active planetary scientist to the general public .
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