For some 20 years, astronomers have been discovering exoplanets, or planets orbiting other stars, in various indirect fashions. These discoveries are just as scientific and valid as a visual observance, if not more so. But once in a while there’s a milestone that’s worth noting for the thrill as much as for the science. The first time we actually saw an exoplanet, i.e. directly imaged, in 2008 was one such example. Now we have the first official detection of an exoplanet’s visible light spectrum, courtesy of the HARPS planet-hunting machine and the ESO’s 3.6-meter telescope at the La Silla Observatory in Chile.
The exoplanet in question orbits the star 51 Pegasi, and is roughly 50 light-years away from Earth in the constellation Pegasus. What also makes this discovery noteworthy is that this exoplanet, 51 Pegasi b, is the first one we ever discovered back in 1995 that orbits a normal star like the Sun. For amateur astronomers, 51 Pegasi itself has an apparent magnitude of 5.49 — meaning you can *just* about see it without binoculars or a telescope if you’re under dark skies. Fortunately, we have much more sophisticated instrumentation available to us than the naked eye:
Wide-field view of the sky around the star 51 Pegasi (Credit: ESO)
While a number of techniques exist for finding exoplanets around other stars, the most commonly used for analyzing an exoplanet’s atmosphere is transmission spectroscopy. Using that method, astronomers measure the host star’s spectrum as it’s filtered through the planet’s atmosphere during transit. When the star passes in front of the planet, you can also discover information about the exoplanet’s temperature. Even so, this type of work is exceedingly difficult, thanks to the fact that exoplanets are extremely dim compared with their parent stars, and are often lost entirely in the glow of the latter.
“This type of detection technique is of great scientific importance, as it allows us to measure the planet’s real mass and orbital inclination, which is essential to more fully understand the system,” said Jorge Martins, the leader of the team behind the discovery, in a statement. “It also allows us to estimate the planet’s reflectivity, or albedo, which can be used to infer the composition of both the planet’s surface and atmosphere.
51 Pegasi is estimated to be between 7 and 8 billion years old, or several billion years older than our own Sun. While 51 Pegasi b, the exoplanet, is considered a hot Jupiter and not conducive to life, the idea that an alien civilization could exist and be several billion years ahead of ours in technology is a sobering thought. Scientists are looking forward to making more discoveries with larger and more advanced telescopes, such as ESO’s Very Large Telescope and the upcoming European Extremely Large Telescope. (Who needs model numbers when you have the world’s clearest names, we ask?)
Last week, NASA announced it’s bringing together experts from a variety of scientific fields in a new coalition to search for alien life on planets outside our solar system.
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