In the process, and much to her delight, McArthur discovered a new, smaller planet spinning closely around 55 Cancri. The Neptune-sized planet, called “55 Cancri e,” was the lowest mass extrasolar planet known at the time. It takes a mere 2.8 days to whip around its sun. McArthur, a research scientist in astronomy at The University of Texas at Austin, didn’t gaze for long hours at the night sky to find the planet. What she did do is analyze data—a lot of data—collected from very powerful telescopes. One of these scopes, the Hobby-Eberly Telescope (HET) located at the McDonald Observatory, took snapshots of the 55 Cancri system for 100 days over a 190-day period. “No one else could do this at that time,” McArthur said. “We had the capability to tell a big instrument to look at the system every day.” The HET measured the star’s wobble, which is caused by the gravitational pull of its planets. The wobble causes light reaching Earth to shift in color. By measuring the star’s color shifts, its planets’ masses and orbits could be determined. McArthur then modeled the solar system in a novel way, by combining the HET data with data from NASA’s Hubble Space Telescope and the Lick Observatory in Northern California. “Barbara combined different data from different telescopes,” said Fritz Benedict, senior research scientist at the McDonald Observatory. “This had never been done in the past and that’s extremely powerful. That’s the way she could dig out this tiny planet.”
“We knew there were supposedly three planets,” McArthur said. “When we looked at the data, we found that there was this other pattern of 2.8 days in the data, which was really cool.” That 2.8-day pattern was the footprint of the new planet, 55 Cancri e, which McArthur pulled out of the weeds of data like an Easter egg. McArthur’s discovery made 55 Cancri the first four-planet extrasolar system that we know. Not only does the system boast a whopping four planets, but one of these is a Jupiter-sized planet orbiting at a Jupiter distance from the sun. “This is the closest analog to our solar system, because it has this Jupiter-like planet and the three inner planets,” McArthur said. This makes the 55 Cancri system a premier laboratory for modeling planetary system formation and evolution and for learning more about our own solar system. Lee Clippard This article originally appeared in the Spring 2006 issue of Focus on Science, the magazine for the College of Natural Sciences. Related Sites
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