Five ‘Holy Grails’ of Distant Solar Systems

Angelle Tanner
Angelle Tanner

Angelle Tanner, a post-doctoral scholar at JPL and Caltech, studies planets in distant solar systems, called extrasolar planets. The golden prize in this field is to find a planet similar to Earth - the only planet we know that harbors life. While more than 350 extrasolar planets have been detected, most are gas planets, with no solid surface. Many are located in orbits closer to their parent star than Mercury is to the sun. In other words, not very similar to Earth.

Here’s Tanner’s short list of what she and her colleagues would love to find in another planet - the elements that might enable life on another world. With the powerful tools scientists have now and with new technology and missions coming soon, the odds are going up for finding an Earth-like planet, if one is out there.

Tanner’s top five “holy grails” of extrasolar planet research are hoped-for findings that she predicts will happen within the next 15 years.

1. First planet that weighs the same as Earth

Artist’s concept of an extraolar planet.
Artist’s concept of an extraolar planet.
Image credit: NASA/JPL-Caltech

Although most planets discovered have been giant gas planets with no surface, a handful of rocky planets, called super-earths, have also been detected. Super-earths are akin to Earth in their rocky make-up, but with a mass up to 10 times that of Earth.

There is no reason these planets could not host an atmosphere or even life as we know it. The discovery of a true Earth clone – Earth-like in size and make-up — could happen within a year or two. NASA’s recently launched Kepler mission has the ability to find planets as small as Earth.

2. First Earth-sized planet in the ‘habitable zone’

The so-called habitable zone is the area around a star where a rocky planet could have the right temperature to have liquid water on its surface. In our solar system, Earth sits in the habitable zone. Venus sits just inside the habitable zone and is too hot while Mars is just outside and too cold. Finding an Earth-sized planet is this geographically desirable location is the next big step in extrasolar research. One super-earth has already been detected near to its parent star’s habitable zone and it is only a matter of time — using existing technologies –- before a planet is found in this friendly environment. Ground-based telescopes and NASA’s Kepler mission are searching stars within a few hundred light years of Earth right now.

3. First atmosphere on a rocky planet

A planet’s atmosphere, along with other factors, helps determine whether a planet could sustain life. For the past few years, astronomers have studied the atmospheres of Jupiter-like, extrasolar planets. These gas giant planets have hydrogen-rich atmospheres inhospitable to life as we know it. However, many of the techniques developed for studying gas giants could be used to study the atmospheres of super-earths. This would mark an important step in beginning to understand the environment of rocky planets.

4. First hint of habitability and life

Once astronomers have enough Earth-sized planet atmospheres to study, they will be looking for biosignatures – indicators in a planet’s atmosphere that the planet might be hospitable to or even support life. Some of the molecules they will be looking for include water vapor, methane, ozone and carbon dioxide. NASA’s James Webb Space Telescope, scheduled to launch in 2014, will provide scientists with the sophisticated instruments needed for these potential observations on super-earths orbiting small stars. Assuredly, astrobiologists will be studying such data for years to come since potential life may, or may not be, in a form we expect. Keeping an open mind is critical.

5. The unexpected

The final grail — the unexpected. The history of science is marked with findings that were never predicted. As in all fields of science and exploration, it’s what we don’t know that will be the most exciting.

For more information about extrasolar planets, visit

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    11 Responses to “Five ‘Holy Grails’ of Distant Solar Systems”

  1. auntie joann Says:
    June 11th, 2009 at 9:44 pm

    If anyone can find that earth-like planet, Dr. Tanner can do it with her wonderful intellect. I have been following her work for many years. Thank you for this very fine article. It provides us with great things to ponder.

  2. Sarah Sims Says:
    June 12th, 2009 at 6:39 am

    Great top five! You rock!

  3. Marguerite Sims Says:
    June 12th, 2009 at 7:02 am

    Just read the full article at work. Love it! So proud of you!!! Keep on searching!!

  4. FloridaDave Says:
    June 14th, 2009 at 4:27 pm

    While the manned space program has had my support from its beginning,the accomplishments of JPL in the exploration of ‘the final frontier’ have been extraordinary.It is truly a quest of knowlege for knowlege’s sake ,which for Me is a worthy and thrilling endevor. Ms. Tanner’s ‘final grail’- the unexpected- is the biggest point. Scientists love to be surprised -it’s what made them become scientists and continue to work hard to figure stuff out.I respect Ms Tanner and all like her at JPL and continue to share in thier awe and pride in thier work.

  5. James Says:
    June 21st, 2009 at 2:35 pm

    someone needs to design and build large space stations designed for solar orbit with ablitiy to move to and stay in ideal habitable zones

  6. Alex N Tsukernik Says:
    July 1st, 2009 at 9:40 am

    I really do believe that the American space program, The Canadian space program,
    and the overall world space program could really benefit from the continuing improvements in the 3 significant areas: Space tourism, Astronomy, and SETI.
    The reasons are because: Space tourism will give the space organizations the needed boost and the economic stimulus to get the world’s people interested in venturing to the outer reaches of Earth orbit and eventually colonozing space.
    Astronomy will expand our horizons by discovering new locations like using the transit method in order to discover extrasolar planets. Including Earth like planets solar systems, and galaxies. SETI: The search for Exta Terrestrial Intelligence, includes the SETI League and the SETI@home. As the name suggests they search for the signals of Intelligence from other non terran galactic sources throughout the universe. The Astrological factors that relate to Astronomy, usually with the study of the constellations could become somewhat useful too.

  7. Jose C. Says:
    September 2nd, 2009 at 9:55 pm

    Wondering here about that super-earth found near its parent star´s habitable zone; and assuming it´s outside, beyond, that zone.

    Given its size, ain´t it going to keep its internal temperatures high, way high, warming its surface up, hence making it quite possible for water to exist in liquid form? Then yes, a thick, heavy, high pressure atmosphere would play against it, but still… Maybe that´s exactly what keeps that water from vaporizing ;-) What I mean is that the habitable zone may have to be ‘relocated’ depending on the planet´s size.

    There are other ways of getting liquid water (Europa has to come to mind) and we know that, but I´m not talking about ‘underneath waters’, hard to find from the distance. I´m talking about our usual concept of habitable zone, the area where water would be found on the surface, flowing happily around. Do you account for the planet´s most basic characteristics (that is, potential conditions) when defining ITS habitable zone or is the habitable zone defined in advance, considering and Earth-size planet?

    My ability to sleep rests on your shoulders now ;-P

    JPL Astronomer Geoff Bryden responds:

    Determining the location of the habitable zone (i.e. where planets can have liquid water on their surfaces) is complicated. While there is a simple formula that can be used as a rough approximation, the detailed properties of the planet will affect the exact result. Planet size certainly matters, but probably not as much as its atmosphere. At the Earth’s location around the Sun, for example, a piece of black dust will reach a temperature of 6 degrees Celsius. The Earth reflects about a third of the incoming sunlight, an effect that would reduce its temperature to -20 degrees. But then you also have to consider effects of the atmosphere (the warming greenhouse effect and the cooling hydrological cycle) which brings things back up to maybe 15 degrees (and rising) for the current Earth. Venus, meanwhile is about the same size as the Earth but is much much hotter because of its
    different atmospheric composition.

    The latent heat inside of the planet can contribute to the overall energy balance (like for Jupiter), but it shouldn’t be a major factor for a super-Earth-sized planet near its habitable zone.

  8. Paul Ketterer Says:
    December 29th, 2009 at 5:16 pm

    I believe quasars are the result of two black holes caught in a deadly embrace where the relative velocities are very high. As gravity draws them closer and close their speed increases dramatically. If they are of sufficient size and have enough relative speed, the crushed mater is ejected in two jets. I believe besides the energy ejected, hydrogen is recreated. Think of hydrogen atoms packed nucleus to nucleus in a pancake fashion being ejected along the axis of rotation. The extreme pressure at the center of the black hole forces the atoms into this alignment. They have no choice but to be ejected. Thus the entire process of cosmos starts again.

  9. johnny Says:
    May 12th, 2010 at 8:47 pm

    will the discovery of another life change the way we look at life, and how will this affect society?

  10. gruzoperevozki Says:
    May 9th, 2011 at 6:48 am

    Интересная статейка, но как по мне, можно было бы и глубже капнуть..)

  11. Debrah Says:
    December 27th, 2011 at 6:32 pm

    We defitnliey need more smart people like you around.

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