Space.com reports that a milestone has been reached in the discovery of planets orbiting other stars.
The 500th alien world appears to have been discovered, according to extrasolar planet trackers.
Less than 20 years after confirming the first planet beyond our own solar system, astronomers have bagged exoplanet No. 500. The milestone was reached Friday (Nov. 19), according to the Extrasolar Planets Encyclopedia, a database compiled by astrobiologist Jean Schneider of the Paris-Meudon Observatory.
As of today (Nov. 22), the count stands at 502 alien worlds, the database reports.
The 500th extrasolar planet was reported in the midst of the discovery of several others. And there's always the risk a previous discovery turns out to be a false alarm, dropping the count.
For such reasons, it makes little sense to permanently anoint one particular world as "exoplanet 500," Schneider told SPACE.com.
That being said, the 500th alien planet currently appears to be one of four newfound extrasolar worlds, based on Schneider's list. They appear on the list just after another extrasolar planet, HIP 13044 b, which astronomers announced last week to be from an alien galaxy.
All of the newfound planets are less massive than Jupiter (they range between 15 and 50 percent of Jupiter's mass), and the planets' distances from Earth range from 58 light-years to 196 light-years.
The find comes less than two months after another watershed moment — the discovery of the first potentially habitable extrasolar planet. And astronomers are sure to hit other big milestones soon, as data rolls in from instruments like NASA's planet-hunting Kepler space observatory.
"In some sense, 500 is an artificial milestone," said Jon Jenkins of the SETI (Search for Extraterrestrial Intelligence) Institute. Jenkins is the analysis lead for the Kepler mission.
"It's much more fun to watch the nature of the discoveries change over time," Jenkins told SPACE.com. "The variety of planets we've discovered has also increased."
Astronomers aren't just discovering scorching-hot gas giants anymore, he added. They are finding smaller, rocky worlds, too — planets that could be a lot like Earth.
There's more at the link.
Dang, these astronomers are making progress! I can remember when they announced they'd found the very first extra-solar-system planet, back in 1988. That was disputed for a long time until it was confirmed, but another discovery in 1992 put the existence of extrasolar planets beyond doubt. Now they've counted over 500 of them! I guess I won't live to see any of them, but who knows? Two or three generations from now, children may be growing up with the option of taking a one-way ride out of our solar system into the great unknown, to colonize a planet from which they'll never return.
How I'd love to have that opportunity! What an adventure!