This week, a team of astronomers at the Keck Observatory announced the discovery of Gliese 581g, a planet orbiting Gliese 581, a red dwarf star twenty light years away (and part of the constellation Libra). Gliese 581g is one of six planets that have been detected around this star, but it is the first that seems to "fit" the requirements for life, which led Steven Vogt to term it the "Goldilocks planet."
Vogt, one of the leads on the team that discovered Gliese 581g, is a professor of astronomy and astrophysics at UC Santa Cruz and a member of the Science Buddies Advisory Board.
Goldilocks is "a well-worn analogy," said Vogt, "but in this case it fits. We had planets on both sides of the habitable zone—one too hot and one too cold—and now we have one in the middle that's just right."
Similar in size to the Earth, Gliese 851g is orbiting in the "habitable zone" around the star, a distance not too close and not too far away—a distance where liquid water could be found. Astronomers describe the planet as "potentially habitable," and one media account of the news included this headline: "Odds of Alien Life on Newly Spotted Exoplanet are '100 Percent' Says Its Discover."
According to reports, Gliese 581g has a nearly circular orbit of almost 37 days and a mass 3 to 4 times that of the Earth. According to Vogt, the increased mass potentially indicates that Gliese 581g has a rocky terrain—and enough gravity to anchor an atmosphere. The planet does not rotate, however, as the Earth does. Instead, it is "tidally locked" to the star. This means that one side of the planet is always in daylight and one side is always in darkness. This might also mean that the likelihood of life on the planet sits somewhere in the middle.
The Powerful Keck
Astronomers deem the discovery of Gliese 581g as "fast," but time and distance are relative when it comes to astronomy and astrophysics. The news of Gliese 581g emerges based on 11 years of observations at the Keck Observatory by a team of astronomers led by Vogt (University of California, Santa Cruz) and Paul Butler (Carnegie Institution of Washington D.C.).
Using the Keck's HIRES spectrometer, the team was monitoring changes in the radial velocity of Gliese 581, changes that can indicate the presence of an orbiting planet. The process is time consuming. "It's really hard to detect a planet like this," Vogt said. "Every time we measure the radial velocity, that's an evening on the telescope, and it took more than 200 observations with a precision of about 1.6 meters per second to detect this planet."
The team's radial velocity observations were balanced by night-to-night "brightness measurements" conducted by team members using robotic telescopes at Tennessee State University. The brightness studies offered a way to ensure the radio velocity changes were indicative of a new planet and not due to other star activity.
The Keck Observatory sits at the top of Hawaii's dormant Mauna Kea volcano where the twin Keck telescopes offer astronomers an unparalleled precision view into distant space. Standing over eight stories tall, and with primary mirrors that are 10 meters in diameter, these are the world's largest optical and infrared telescopes.
Students interested in exploring the use of sophisticated astronomy equipment to make observations may find the following Science Buddies project ideas illuminating:
- Using the Solar & Heliospheric Observatory Satellite (SOHO) to Measure the Motion of a Coronal Mass Ejection (Difficulty: 7-9)
- Using the Solar & Heliospheric Observatory Satellite (SOHO) to Determine the Rotation of the Sun (Difficulty: 7)
Or, to really get down to the nitty-gritty of what's involved, start from the ground up and build your own telescope (Difficulty: 9-10).
Official Keck announcement: