Examining Exoplanet Data

As many of 15 percent of all stars might host Earth-like planets, John Armstrong, assistant professor of physics at Weber State University, Ogden, told members of the Salt Lake Astronomical Society Tuesday evening.

By Earth-like, that doesn’t mean all will be in a star’s habitable zone; it means Earth-like in size. But planets that are larger than Earth also may be capable of hosting aquatic life, he said Tuesday evening.

Armstrong, who spoke during the group’s regular monthly meeting in the University of Utah’s Engineering/Mining Building, is among 40 researchers around the world who participate in NASA’s Virtual Planetary Laboratory, modeling types of climates that may exist on various kinds of extrasolar planets.

These scientists have begun studying data that NASA released on Feb. 2 from the Kepler space telescope project. Covering only the first four months of Kepler’s work, the data include 1,235 planet candidates discovered around 15,553 stars examined by Kepler.

[WSU physicist John Armstrong discussing Kepler findings Tuesday night at the monthly meeting of the Salt Lake Astronomical Society. Photo by Cory Bauman]
Kepler is measuring light from stars in the direction of the constellations Cygnus and Lyra. This location within the Milky Way was chosen because “they could get the most stars in one field of view without getting too many stars within the field of view,” he said.
The orbiting telescope is designed to continuously “stare at” the same relatively small region of space and measures the stars’ brightness, he said. When a planet moves between the spacecraft and the star, the star’s light dims. A repeated pattern of dimming could indicate the passage of a planet or a dwarf star; this is noted as a candidate-planet.
Among more than 1,200 planetary candidates found so far, 68 are Earth-size, 288 are called super-Earth-size (up to twice the mass of our planet), 644 are Neptune-size and 165 are Jupiter-size. Of the total, 54 orbit within the habitable zones of their stars, where liquid water could exist, according to NASA.
“There is a handful, probably four or five, Earth-like planets in the habitable zone,” Armstrong said.
Many more planetary candidates are expected to turn up as Kepler continues its studies. By the end of the project, perhaps 500 planets will be discovered that are Earth-like in size. “Mass plays a very important role here,” he said.
What about planets that are twice as large of Earth but still in their stars’ habitable zones? “These super-Earths are incredibly wet,” having pulled in many icy comets as they were formed. Because they are close enough to their stars that the planets are not frozen, they may contain deep oceans.
On super-Earths, “there could be life, but it wouldn’t be land-based life,” he said.
Armstrong’s group has found that in some situations, wildly-tilted planets may make a planet more habitable. One constant necessary for life may involve the amount of water present. “Is there a correct amount of water that a planet needs to have?” he asked. The answer seems to be yes, he added.
“What we’ve found out is that Earth could actually be a desert planet,” compared with others in the habitable zone. According to Armstrong, super-Earths “have a deeper gravity-well to suck in more asteroids and comets” that are loaded with ice.
Large moons, possibly Earth-size, could orbit huge planets in the habitable zone.
Salt Lake Astronomical Society monthly meetings are open to the public and feature speakers who are knowledgeable about astronomy. To learn more about the group, click HERE.

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