Eyeing planets — near and far


Tom BurnsStargazing

Recently, we have been the beneficiaries of two major media events related to space exploration. One was certainly worthy of the media attention. The other one was hyped beyond all recognition.

Decades in the making, the New Horizons spacecraft finished 9½ years of its long journey to study the dwarf planets and other objects that populate our outer solar system.

Its close encounter with Pluto yielded a wealth of data that will take months to transmit back to Earth. The first images were a startling look at the icy mini-planets that populated our solar system before the major planets were formed and, in fact, clumped together to form the larger planets.

One thing is certain. The dwarf planets are fundamentally different from the two categories of planets that make up the eight major planets. Pluto is mostly a ball of very cold ices – frozen water and methane. The “terrestrial,” or Earth-like, planets are larger balls of mostly rock and metal. The “Jovian,” or Jupiter-like, planets are enormous ball of mostly liquid.

Pluto’s methane accounts for its newly discovered atmosphere, a haze around the planet beautifully imaged by the space probe for the first time.

Even at Pluto’s great distance from the sun, its surface is feebly struck by solar energy. The high-energy ultraviolet portion of that energy breaks down some of the planet’s methane and forms particles of more-complex hydrocarbons like ethylene and acetylene.

Those particles fall like snow toward the surface through Pluto’s very cold atmosphere and condense into an atmospheric haze. Eventually, the particles get large enough to fall to the surface as a reddish-brown gunk, which coats parts of the planet and give it its distinctive red-brown color.

Two discoveries surprised astronomers. One was the presence of mountain ranges that are perhaps only 100 million years old. Also, New Horizons reveals high cliffs and enormous troughs and canyons. Given Pluto’s age, over 4 billion years, the “new” mountains and other features suggest relatively recent geological activity. Pluto is out there in the deep freeze of space far from the sun. What geological processes could have been happening so long after Pluto’s formation?

Another surprise, perhaps related, is the relative lack of craters. Other objects have clearly bombarded Pluto. Some of its moons were probably formed from such impacts. What recent geological activities account for the lack of craters that must have been created earlier in Pluto’s history?

Only a fraction of the data from New Horizons has been downloaded to Earth. Time and analysis of that information may yield answers.

Yet another “Earth-like” Exoplanet?

The second media event received just as much media attention. NASA released another wave of data from the Kepler Space Telescope, which is tasked with discovering exoplanets, planets orbiting stars other than our sun. Among that information was the discovery of Kepler 452b, widely described as “the most Earth-like planet” discovered thus far.

Nonsense. But even more nonsensical was the raft of comments, including some on our local media, that “with so many Earth-like planets, there has to be a lot of life out there.”

The Kepler Space Telescope looks for planets by measuring minute changes in the brightness of stars. As a potential planet passes in front of the star, the star dims slightly. The planet’s orbit is determined by the length of its passage in front of the star, called a transit, and the time between transits. From the combination of all those bits of information, the planet’s average distance from the sun and its mass is calculated. From that information, astronomers can take an educated guess about the planet’s diameter and composition.

The measurement of the star’s tiny brightness changes takes an extremely sensitive telescope. Kepler is certainly sensitive, but not quite sensitive enough to give an exact figure. The best it can do is a range of numbers. Thus, the new planet is anywhere from 3-7 times the mass of Earth, and anywhere between 1.5 times Earth’s diameter at the low end and nearly the diameter of a small gas-giant planet like Neptune.

Big difference. NASA tends to tout the low end of the approximation, and the media eat it up. But NASA-associated scientists are more cautious. One condition for life is probably a solid surface. Given the range of sizes, the new planet might have a solid surface or it might be a giant giant. Jon Jenkins of NASA’s Ames Research Center estimates its chances of having a solid surface at between 49 and 62 percent.

Also, much has been made of the planet’s orbit. It may, in fact, be within the “habitable zone,” but the term is misleading. It actually means that the planet might be the right distance to harbor liquid water. However, the exoplanet is on the hairy edge of being too close and too hot. Also, you’d need a solid surface to have an ocean, and that is far from certain.

The discovery of Kepler 559b is certainly a step in the right direction. At best, Kepler 552b has become a candidate for future space telescopes, which may have the increased sensitivity to determine its actual size and orbit.

In the meantime, let’s all calm down. No planet, besides Earth, of course, has been discovered that could — with any degree of certainty — harbor life. While we wait for answers, let’s revel in our uncertainty — and continue the search for answers.

This Month’s “Astronomy and …” talk at Perkins Observatory: No planet has been more singed by media exaggeration than Mars. Paul Kostyu of Ohio Wesleyan University’s journalism Department will discuss that and other issues on Thursday, Aug. 6, starting at 8 p.m.. His talk is titled “Astronomy and Journalism: Covering the Martian Beat.”

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Tom BurnsStargazing

Tom Burns is director of the Perkins Observatory in Delaware.

Tom Burns is director of the Perkins Observatory in Delaware.