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Duo at NMSU Stars In Planet Discovery

Posted on: Wednesday, 1 September 2004, 06:00 CDT

Las Cruces astronomers Tom Harrison and Joni Johnson are not your typical planet hunters.

The New Mexico State University researchers' specialty is the meticulous calculation of the distance to stars. But the duo's star skills played a critical role in the discovery of an important new planet this spring.

The discovery, announced at a NASA news conference Tuesday, marks the first time astronomers have found a medium-sized planet -- between giant Jupiter and relatively small Earth in size -- outside our solar system.

In addition to expanding our knowledge of what types of planets can form around other stars, the discovery demonstrated new techniques that eventually may prove useful in the search for Earth- like planets around other stars.

Using the Apache Point Observatory near Cloudcroft and a tiny telescope on the NMSU campus in Las Cruces, Johnson and Harrison were able to calculate the distance to more than half a dozen stars crucial to their analysis.

"It's essential but tedious," Harrison explained in a telephone interview Tuesday afternoon.

"Tedious" could actually describe the whole planet-hunting enterprise, but the results have revolutionized our understanding of our solar system's place in the cosmos.

Before 1995, the only known planets were our neighbors orbiting our own sun, and astronomers hotly debated what it took to form planets and how common they might be around other stars.

Over the last decade, the increasingly frequent discovery of enormous planets the size of Jupiter orbiting other stars has made clear that many other stars have the right stuff for planets to form around them.

The latest tally, with Tuesday's announcements, is now up to 127 so-called "extrasolar planets."

But while astronomers assumed that smaller planets, perhaps Earth- like ones, must be out there, finding them has been tough.

The breakthrough discoveries, announced Tuesday by two independent research teams at the NASA news conference, used new techniques that allowed the astronomers to be much more precise in measuring the orbits of the newly discovered planets.

Harrison and Johnson worked with Barbara McArthur of the University of Texas, Austin, on the discovery of a Neptune-sized planet -- some 14 times the mass of Earth. The second discovery, also of a Neptune-sized planet, was made by Paul Butler of the Carnegie Institute of Washington and Geoffrey Marcy of the University of California, Berkeley.

The researchers cannot see the planets directly.

Instead, they infer their presence by precisely measuring wiggles in the position of a star.

As a large planet orbits a star, its gravity tugs it slightly out of position.

By measuring the star's position as it moves ever-so-slightly against the background of more distant stars, the astronomers can calculate how large a planet is doing the tugging. That is why finding larger planets has been easier -- they give the stars a bigger gravitational tug.

For the new calculations to work, the astronomers needed to know the distance to the background stars they were using in the calculations.

For that job, McArthur's team turned to Harrison.

"They actually called me up in a bit of a panic last March," he recalled.

Harrison got three hours on the Apache Point Observatory's main telescope in May, and Johnson did the actual observations. Harrison then did a second set of observations needed to complete the calculations in June, using a small telescope located on the south side of the NMSU campus.

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