Hunting for Planets

In July, NASA’s New Horizons space probe captured dazzling images of the dwarf planet Pluto and its moons during a 31,000-mile-per-hour flyby. Surprising even some experts, the pictures revealed a vast variety of geologic features from frozen plains to streams. In the scientific community these photographs are provoking as many questions as they are answering.

“Pluto is the best known member of a class of objects that lurk in the exterior of our solar system,” says Cullen Blake, Assistant Professor of Physics and Astronomy. “Before the New Horizons photos, we conceived of these planets as big, dirty balls of ice. Now we realize that they are not featureless and barren because they have mountains and canyons on the surface.”

The conundrum for people in the scientific community is how this geology came about, Blake explains. On Earth, geologic change is caused by environmental forces such as climate systems and atmospheric circulation—but just what is creating these features on planets like Pluto?

The Pluto pictures from the New Horizons were reaped via a payload of state-of-the art technologies aboard the probe, including spectrometers capable of infrared and ultraviolet imaging. Advanced imaging techniques are increasingly important to exploring and mapping space as astronomers, Blake among them, focus their investigations on a burgeoning enterprise: the discovery and documentation of thousands of heretofore unknown smaller stars outside Earth’s solar system and the exoplanets that orbit them.

Blake’s lab at Penn operates a planet-hunting telescope known as Minerva-Red, which is now installed at the Fred Lawrence Whipple Observatory in Arizona. Minerva-Red is part of a national astronomy initiative, the Minerva project, which is an array of low-cost telescopes that are designed to discover planets orbiting stars other than the sun.

“There is new evidence that there are planets orbiting little stars, and among these might be planets that are closest to our own solar system,” Blake says.

Blake is particularly fascinated by information culled from NASA’s Kepler Mission, which the agency describes as “a search for habitable planets.” The habitable zone is the range of distances from a star where liquid water might pool on the surface of an orbiting planet because it is neither too hot nor too cold. To date, Kepler has identified more than a thousand small planets and solar systems in our Milky Way galaxy, including one dubbed “Earth’s twin.” The so-called twin is a planet roughly one and half times the radius of Earth and, according to NASA, it is the first Earth-size planet known to orbit a star in the habitable zone.

“The takeaway is that our solar system is not unusual,” Blake says. “We now know that a huge percentage of stars have planets revolving around them.”

Working with two graduate students and an undergraduate, he is currently building a device to measure motion, which he calls “wobbles,” in small stars. These stellar wobbles are caused by unseen planets.

“If the stars wobble, we can infer that the planets exist,” he says. “We are working on two independent pieces of hardware that work together with the telescope at the Whipple Observatory to find new planets.”