Neighborly star
Earth’s nearest habitable neighbor may literally orbit our nearest stellar neighbor.
According to NASA’s exoplanet webpage, we know of 3,779 planets orbiting stars other than our sun, with 2,737 more candidates awaiting confirmation. And that is just the tip of the exoplanet iceberg.
The large majority of confirmed and suspected exoplanets are discovered by the transit method. A telescope in space or on Earth stares at a star and watches for small drops in the light output that indicate a planet is passing in front of, or transiting, the star. There are many ways a star’s light may vary, but each has a specific signature as to how the brightness varies. Planetary transits cause a unique alteration in the star’s light.
This method can only detect planets whose orbits lie along our line of sight, and that’s quite unlikely. That astronomers have found so many exoplanets when they can only detect such a tiny fraction of potential candidates implies a huge number of exoplanets exist. In fact, astronomers estimate based on the known sample that the 400 billion stars in the Milky Way average 1.3 planets each. That’s a lot of planets. It turns out that one exoplanet is literally right next door. The closest star system to us is Alpha Centauri. It actually consists of three stars. Two of them, Alpha Centauri A and B, both roughly the size of our sun, orbit each other rather closely. The third member, named Proxima Centauri, orbits those two in a wide, 550,000year orbit. Proxima comes closer to us than any other star, 4.2 light years at its closest.
Proxima is known to possess a planet only slightly larger than Earth. And the planet lies in the star’s habitable zone, where the star provides enough heat to allow liquid water, as on Earth. Since Proxima is a red dwarf star, much smaller than our sun, the planet must orbit close to the star to be warm enough. The planet’s orbit takes only 11 days. But it is exactly in the middle of Proxima’s habitable zone. Being so close to the parent star, it is probably tidally locked. One side constantly faces the star, just like only one side of the moon always faces Earth. This means one side is in constant daylight, the other perpetual night.
Anthony Del Genio, a planetary scientist at the NASA Goddard Institute for Space Studies, led a group of scientists doing computer simulations on Proxima B. They wanted to know if the planet could support life. They made the reasonable assumptions that the planet had an atmosphere as thick as Earth’s and enough water to form an ocean. Using computer models like those used by researchers to study climate change on Earth, they found that under a broad range of conditions, the planet can sustain liquid water even on the night side. On Earth, where there’s water, there’s life. “The major message from our simulations is that there’s a decent chance that the planet would be habitable,” said Del Genio.
Our nearest habitable neighbor may literally orbit our nearest stellar neighbor.
October highlights: This month, the moon makes two house calls to a bright star cluster. At 4 a.m. Thursday and again at 6 a.m. on Oct. 31, the half-full moon sits close to the Beehive star cluster in Cancer, the crab. The Beehive is one of the brightest star cluster visible from Oklahoma and the two should make a delightful sight in a pair of binoculars or a low power view in a telescope.
During the early morning hours of Oct. 22, we pass through dust debris from Halley’s comet, creating the Orionid Meteor Shower. Orion is the brightest constellation visible from Oklahoma. At 5 a.m., when the activity is near its peak, it will be high in the south. By that time, the bright moon will have set, making for a great view of the shower. You’ll need to get far away from city lights for your best view. You should be able to see one meteor every three to four minutes.
Planet visibility report: As the month begins, brilliant Venus and nearlyas-brilliant Jupiter sit not far apart in the west after sunset. Venus may be blocked if you have trees or buildings along your western horizon. Saturn and Mars are also up at sunset. Saturn is in the south and Mars in the southeast. Mercury finally enters the evening sky, but is still too low to see. Venus dives quickly into the evening twilight, while Mercury rises farther from the sun. The two cross on Oct. 15, but both will be tough to find in the twilight glow. Jupiter is not much higher as it slowly slips into the oblivion in the evening twilight. On the Oct. 28, with Venus behind the sun, Mercury passes below Jupiter, both visible after sunset if you have a clear view of the horizon. Saturn and Mars remain in the evening sky all month. New moon occurs on Oct. 8 with full moon following on Oct. 24.