The centuries-old quest for other worlds like our Earth has been rejuvenated by the discovery of hundreds of exoplanets--planets orbiting other stars.
Less than a generation ago, astronomers had no tools or methods to detect exoplanets. Today, thanks to projects like NASA's Kepler mission, we know that exoplanets abound. The Kepler mission was specifically designed to survey our region of the Milky Way galaxy for exoplanets and to explore the structure and diversity of these planetary systems. Kepler is potentially able to detect Earth-sized and smaller planets in the habitable zone around each star.
On Monday, June 4, Dr. Debra Fischer, professor of astronomy at Yale University, visited Maui to give a talk called "Searching for Earths" at the University of Hawai'i Institute for Astronomy (IfA) in Pukalani. An internationally recognized expert on exoplanets, Dr. Fischer is part of a team of astronomers who have found many of the exoplanets discovered to date. She has also helped initiate the Planet Hunters project.
Maui Astronomy Club President Rebecca Sydney cheers as a student views the transit of Venus on Tuesday, June 5, at Kama‘ole III Beach Park in Kihei. This particular planetary alignment of the sun, Venus and Earth will not occur again for more than 100 years. However, transits of planets circling other stars in our galaxy can now be used to discover these so-called “exoplanets.”
Photo: Cindy Schumacher
"Since our online citizen science project Planet Hunters launched last December, over 40,000 Web users have been helping professional astronomers analyze the light from stars in the hopes of discovering Earth-like planets orbiting around them," she said. "We simply have too much data nowadays for the professionals in this field to analyze by themselves."
Citizen users analyze real scientific data collected by NASA's Kepler mission since its beginning in March 2009.
"This is the first time that the public has used data from a NASA space mission," said Dr. Fischer, affirming that with each new round of data there are more discoveries.
We now have clear evidence for substantial numbers of three types of exoplanets: gas giants, hot-super Earths and ice giants.
"The challenge is to find terrestrial planets, especially those in the habitable zone of their stars, where liquid water might exist on the surface of the planet," she said.
When a planet passes in front of a star as viewed from Earth, the event is called a transit. For example, in our own solar system, the planets Venus and Mercury occasionally transit across the face of the sun as seen from Earth. In fact, on Tuesday, June 5, the day after Dr. Fischer's talk at IfA, a rare transit of Venus occurred as if on cue, and was viewed with much enthusiasm on Maui. The event perfectly illustrated an important planet-hunting technique.
A transit is seen as a small black dot creeping across the sun, partially blocking the sunlight as the planet moves between the sun and us.
"The Kepler mission finds planets by looking for tiny dips in the brightness of a star when a planet crosses in front of it," said Dr. Fischer.
The size of the planet is then found from the measured dimness and the known size of the star. From this information, the question of whether or not the planet is habitable can sometimes be answered.
Beginning with our own solar system, Dr. Fischer explained that the sun is one of billions of stars in our galaxy and that the Milky Way one of billions of galaxies.
"We are such a tiny speck in a vast universe!" she said.
Dr. Fischer has been involved with a project using a spectrometer her team developed to search for low-mass, rocky planets around Alpha Centauri A and B, the nearest star system to Earth.
"Spectroscopy, astrometry and the Doppler technique are powerful tools in helping to determine the potential habitability of the worlds we find. Astronomers are looking for the conditions and chemical signatures we associate with life, such as liquid water," she said.
Dr. J.D. Armstrong, Maui technology outreach specialist for the IfA, is excited about the planet hunting that our young student scientists are conducting from the islands.
"Through the IFA educational outreach program, students in Hawai'i are given access to research-grade telescopes, such as the Faulkes telescopes, and are able to observe any time of day from anywhere in the world with an internet connection," Dr. Armstrong said.
"By using the transit method, the students can determine an exoplanet's size and distance from its star," he said. The repeated occurrence of transits is the major diagnostic test that determines whether the observed dimming of the star is really from a planet in the first place.
"During last year's HI STAR program, students were able to help confirm a hot Jupiter-sized exoplanet orbiting close to its star," he said. "They actually discovered a new planet many light-years from Earth."
"Think about what these students are doing," said Dr. Armstrong. "They get to work with astronomers, 'to explore strange new worlds, to seek out new life and civilizations, to boldly go where no man has gone before!'" Yes, "Star Trek" has been a big influence on a whole generation of scientists.
Dr. Armstrong and Dr. Fischer both agree about the importance of astronomy's role: "We're looking out, looking up, looking back in time, and understanding ourselves better for that."
For more information, go to www.ifa.hawaii.edu/haleakala and planethunters.org.