Search for habitable planets topic of talk

NASA Ames Research Center astrobiologist and research scientist Tori Hoehler, Ph.D., has been searching for exoplanets in the “habitable zone” for 17 years.

In a March 21 presentation to the Morning Forum of Los Altos, “Exoplanets: The Hundreds of Confirmed Planets Outside Our Solar System,” he shared the criteria and success rate.

Hoehler earned a Bachelor of Science in chemistry and a doctorate in marine chemistry and biogeochemistry from the University of North Carolina. He has worked at NASA Ames as a research scientist since 2001. He was named a Kavli Frontiers of Science Fellow at the National Academy of Sciences and serves as a collaborating research scientist at the Mars Science Laboratory and a member of the Europa lander science definition team.

Exoplanets are planets that orbit stars, similar to the way Earth orbits the sun. When Hoehler joined NASA Ames, there were only two known exoplanets. Thanks to the Kepler telescope and an explosion of technology, more than 2,000 exoplanets have been identified to date.

The NASA Discovery mission is specifically designed to survey the galaxy to discover Earth-sized and smaller planets in or near the “habitable zone.” Kepler has enabled astronomers to observe the exoplanets as they travel across the light of their companion star. A recent example of such transit was when the planet Venus moved across the sun.

According to Hoehler, astronomers, chemists and geophysicists want to find out which of these exoplanets have the ability to support life. A key requirement is the availability of liquid water, he noted, adding that the exoplanet must be an appropriate distance from its corresponding star to maintain a temperature that will keep its water from freezing. Another requirement is the planet’s chemical atmosphere – for example, water, carbon dioxide and methane that deliver oxygen and support ingredients for life.

In addition to absorbing light from corresponding stars and releasing it into space, scientific teams can analyze the light’s spectrum and the radial velocity of its orbit to determine the exoplanet’s chemical and biological characteristics and its density. For example, how massive is it, and is it composed of metal, rock, gas and water? To date, 25 or 30 exoplanets have been identified as possibly habitable, Hoehler said, and the closest one is only 10,000 light years away.

What scientists don’t know is how much light is absorbed to keep surface temperature intact to enable life and how much is reflected into space.

Hoehler briefly described several other NASA missions that have been exploring answers to the question “Are we alone?”

NASA has launched Mars missions that have traveled a marathon of miles across its surface, collecting rocks, searching for evidence of water, drilling holes in its surface and even appearing in a selfie from the delivery vehicle circling above. The Cassini spacecraft – the size of a large school bus filled with scientific instruments – has recorded waves, storms and eruptions on Saturn as it makes its 12-year journey around the planet. The Voyager spacecraft, launched in 1977, is the farthest away, currently near the planet Uranus.

For Hoehler, pursuing this exoplanet quest captures an exciting combination of chemistry, astronomy, physics and biology.

Morning Forum of Los Altos is a members-only lecture series that meets twice a month at Los Altos United Methodist Church. For a list of speakers and more information, visit

Schools »

Read More

Sports »

Read More

People »

Read More

Special Sections »

Special Sections
Read More

Photos of Los Altos

Browse and buy photos