Date: April 19, 2012
Title: Encore: Earth Clones
Podcaster: Chris Impey
Links: http://planetquest.jpl.nasa.gov/
http://exoplanet.eu/
http://kepler.nasa.gov/
http://www.chrisimpey.com/
This podcast originally aired on January 27, 2010
http://365daysofastronomy.org/2010/01/27/january-27th-earth-clones/
Description: There are over 400 planets know orbiting other star, but most are gas giants like Jupiter and likely to be uninhabitable? How long before we find a clone of the Earth? This podcast talks about the issues involved in detecting terrestrial planets and the likelihood that they will be discovered in the next few years.
Bio: Chris Impey is a University Distinguished Professor and Deputy Head of the Department, in charge of all academic programs. His research interests are observational cosmology, gravitational lensing, and the evolution and structure of galaxies. As a professor, he has won eleven teaching awards, and he has been heavily involved in curriculum and instructional technology development. Impey is a past Vice President of the American Astronomical Society. He has also been an NSF Distinguished Teaching Scholar, a Phi Beta Kappa Visiting Scholar, and the Carnegie Council on Teaching’s Arizona Professor of the Year. Impey has written over thirty popular articles on cosmology and astrobiology and co-authored two introductory textbooks. His first popular book “The Living Cosmos,” was published in 2007 by Random House; his second popular book called “How It Ends,” will be published in 2010 by Norton. He recently was a co-chair of the Education and Public Outreach Study Group for the Astronomy Decadal Survey of the National Academy of Sciences. Impey is a 2009 Fellow of the American Association for the Advancement of Science.
Sponsor: This episode of “365 days of Astronomy” is sponsored by — NO ONE. please consider sponsoring a day or two in 2012 so we can continue to bring you daily “infotainment”.
Transcript:
Chris Impey, Professor, University of Arizona
Welcome. This is a podcast for 365 Days of Astronomy for the year 2010. My name is Chris Impey I’m a professor of astronomy at the University of Arizona. My research is on cosmology but I take a keen interest in Astrobiology, the search for life in the universe. And my topic today is Earth clones – what will it take to find twins of Earth out there in deep space.
As I’m sure you know – the success of exoplanet hunting is phenomenal. In 1995 we knew of no planets beyond the solar system. Now we have over 400. However almost all of those planets are gas giants, Jupiter mass ranging down to Neptune and Uranus mass. Almost certainly they’re uninhabitable, we don’t think there is life in Jupiter or Saturn’s atmosphere. So what’s really interesting is pushing down the mass limit towards terrestrial planets so we can find planets that might harbor biology. What will it take to do this?
Simulations and theory give us the expectation that terrestrial planets exist out in space even though we haven’t found them yet. The current record holder for a low mass planet beyond the solar system is a planet 1.9 times the mass of Earth. However it’s not in the habitable zone of its star. Simulations however suggest that for every gas giant planet that forms at the periphery of a solar nebula there will be a handful of terrestrial planets on orbits much like those of Earth, Venus, and Mars.
If we scale up these numbers to the Milky Way we conclude a phenomenal billion habitable worlds in the Milky Way, including moons of giant planets as well. And possibly a tenth of those or about a hundred million will be planets like the Earth, Earth-clones more or less. That’s an amazing amount of habitable real estate in just one galaxy in the universe.
So how do we find such planets, with four hundred in the bag but none of them Earth-like? Well the most direct method, making an image, is the most difficult. The Earth reflects less than a billionth of the light of the Sun, and as seen from afar would be like trying to detect a firefly in the glare of nearby stadium floodlights. Essentially impossible with current technology. So we can’t image these planets. Also, the Doppler Effect, which has been most successful in finding almost all of the 400 known exoplanets, runs out of steam when it goes to the low mass planets. By the time we get down to a terrestrial planet, the Doppler shift, the wobble on the star caused by the orbiting planet, is a small enough velocity that it can be confused by turbulent motions in the star atmosphere. Essentially noise from the star itself prohibits us detecting earths with the doppler method.
The method that may work, and we hope it will work, is the eclipse method. Every now and then, seen from the right orientation, a terrestrial planet will pass in front of its parent star dimming it very slightly in proportion to the ratio of the area of the planet to the area of the star.
For an Earth-like planet orbiting a Sun-like star, this dimming is tiny, about one hundreth of a percent. That can’t be detected from the Earth. But from space, with the stability of that environment it is possible.
Last year the Kepler spacecraft was launched with the deliberate purpose and agenda of detecting terrestrial planets and Earth clones. Kepler has gone through its early paces and has shown that it has the stability and the sensitivity to detect eclipses by Earth-like planets. It’s staring at a region of sky containing over 100,000 stars and it’ll stare at it for several years trying to detect the momentary dimming of the star. Remember, it’s one hundreth of a percent. Imagine trying to stare at a 100W lightbulb to see if it’d dim by hundreth of a watt. It’s a difficult task but Kepler has shown it’s up for the job.
We’ll have to be patient however. An Earth-like planet in orbit around a Sun-like star will of course transit only once every year. And Kepler will need to see the eclipse recurr maybe twice or three times to be sure it’s detected a real planet. That means, we’ll have to wait a couple of years before Kepler starts announcing Earths. But they are expected.
Nobody really knows how many Earth-like planets Kepler will find. It could be dozens, or it could be as many as hundreds. Meanwhile, we have to look after Earth 1.0. We’re not going anywhere else soon. Even if we find an Earth clone, a place that might be hospitable to life, or a place where we might go and colonize, it’s going to be very far away. Most of the stars that Kepler is looking at are dozens, if not hundreds, of light years away. With current technology, that would take hundreds or thousands of years to get to. Even with a space probe, and we have no way of sending humans that far.
Alpha Centauri, it turns out, is the nearest place we might look for a terrestrial planet, only about 4 light years away. Careful work on that double star system may well find Earth-like planets within the next few years. This whole work of finding Earth clones will put into sharper focus the next stage in the search for life in the universe. Because once we start finding places with all the ingredients for life: energy from a star, organic material and liquid water on the surface, it should only be a matter of time before we can detect the signs of life on one of those planets.
This has been 365 Days of Astronomy, and this is Chris Impey signing out. Goodbye.
End of podcast:
365 Days of Astronomy
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