“The diversity of the phenomena of nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment.”
Johannes Kepler (1571-1630)
NASA’s Kepler mission is getting a lot of media buzz as it continues to search for so-called exoplanets – planets orbiting other stars – that might be able to support human life. Over the 3-4-year life of the mission (which might well be extended), its telescope/photometer will monitor perhaps 100,000 stars in our galaxy.
Interested in how it works? Let’s start closer to home. We’ve been able to see transits of Mercury and Venus across the visible disk of our sun all along. Whenever they pass between us and the sun, we see a little black speck moving across the bright background of the solar disk. There’s also a very slight, but measurable, reduction in the sunlight that reaches us.
The Kepler mission works the same way. The instrument keeps an eye on each star under scrutiny, more or less continuously (transits can be brief!) for an extended period, hoping to spot similar transits as any exoplanets happen to orbit that distant star.
A bittersweet personal note: My college roommate at Swarthmore, Robert Sutton Harrington, was a fellow physics major, destined to be an astronomer. While in college he worked at our Observatory. Swarthmore had a large refracting telescope that was used to study binary stars – star pairs in orbit around one another. [These were detectable by slight changes in distance between them that could be measured on successive photographic images.] Bob would later work at the Naval Observatory where he continued these and similar studies. Early attempts to look for exoplanets involved trying to detect similar small wobbles in the positions of stars occasioned by massive-but-not-quite-stellar-sized objects in orbit around them; this has proved much less satisfactory than the current approach. Bob also spent a lot of effort looking for a tenth planet in our solar system, with no success. However, this and other work has earned him a Wikipedia entry, despite his untimely death in 1993 from cancer.
Kepler astronomers have identified some 1000 or so such exoplanets so far, roughly doubling the number identified to date. They tell us that a most of these planets come in one of three flavors – gas giants; Earthlike but superhot objects in tight, fast orbits; and ice giants. But in addition, the mission scientists are on the lookout for members of a fourth group –those maybe half to twice the size of the Earth, and in a Goldilocks (not too hot, not too cold) temperature regime allowing for the maintained existence of liquid water.
How do they learn all this? From mass of the distant star and the length of time the exoplanet takes to complete an orbit (the time between successive transits), scientists can determine the orbit size. The size of the planet itself is estimated from the dip in the star’s apparent brightness and the size of the star. From the orbit size and the star size, astronomers can calculate the planet’s temperature.
So far the search has identified maybe ten of these. Kepler-22B is one such – at some 2 times larger than Earth, and boasting an average temperature of something like 70 degrees Fahrenheit, it might well have oceans. However, with today’s science, there’s no real way to tell its composition. Does it, like Earth, have continents and oceans, a rocky core, or even life itself? No way yet to tell, really.
That didn’t stop one enthusiastic news report from referring to this as the “new Earth.” The same text reports scientists as saying Kepler-22b holds the best hope yet for “future human habitation.”
Most likely a slip – at best a poor turn of phrase. That hope is slim, because Kepler 22-B is 600 light years away. Doesn’t sound so bad, until we recall that light doesn’t just lollygag along. Instead it zips about at almost 200,000 miles a second. So that planet and its sun are 3000-4000 trillion miles away, about 40 million times further distant than our own sun.
Even with the tantalizing new science buzz that some neutrinos just might go slightly faster than this speed of light – emphasis on neutrinos, and on just slightly faster –you and I shouldn’t be expecting space tourism to get us there anytime soon. As noted back in the early days of this blog, we’re earthlings, till death do us part. So, from this quarter we can expect no escape from the troubled Euro or the declining dollar, from water-resource shortages or declining food margins, from biodiversity reduction and landscape degradation, from tornadoes or hurricanes or earthquakes. And we must still face that marvelous challenge of getting along with each other, and recognizing our mutual interdependence.
On the positive side…if we keep on monitoring Kepler-22B over time, and someday begin to detect a temperature increase over a century or so, maybe we can infer that it like us has humanoids…and they’ve started burning their fossil fuels.