Storms, clouds, and even sun and stars
As far as we're concerned, every other world—whether distant or close to Earth—is an unexplored territory. Some of the new exoplanets can be found right in our backyard—in the constellation of Leo. The "hot dwarf" star Kelt-9b, which lies 4,700 light-years from Earth, shows evidence of auroras—large-scale electromagnetic displays that occur when charged particles that are trapped in the planet's magnetic field are accelerated along magnetic field lines. Kelt-9b is around the size of Jupiter and located so close to its star that it orbits once every seven days!
We often assume that other planets lie at the perfect distance from their stars—that they're ideally placed. But the truth is, very few exoplanets fall into this "sweet spot." Many of them, instead, are near their stars (such as Kelt-9b, which has a very short orbital period) and extremely hot.
There are also more exoplanets out there than the current estimates of Earth-like worlds—which were based on the discovery of one planet around each of a mere 160,000 stars. (Only a quarter of those systems have multiple planets orbiting a single star.) The latest observations, though, have turned up stars that have planets in abundance.
Scientists at the HARPS telescope in the Canary Islands, Spain, report that they've detected 11 new exoplanets around the nearby star Tau Ceti, which is just 11.5 light-years away. These worlds range in size from 1.25 to 1.5 times the diameter of Earth's orbit around our sun. If you were looking for an Earth twin, this would not be the ideal star to choose. But there's more: The HARPS team reports that it has found multiple Earth-sized planets circling four of the systems' seven stars. And there's more news about this stellar system: It was first discovered in 2004. Based on the rate of discovery, we can expect to find another 1,000 planets just like this one.
Now if you were to look through your telescope or Google Earth and scan the skies for bright stars that might harbor planets, you could quickly find new worlds—and perhaps some surprising ones.
For example, a survey of stars that are 1,000 light-years away led astronomers to discover five exoplanets in the Taurus constellation. Three of them (a gas giant, a "hot Jupiter," and an Earth-like world) orbit the small red dwarf star TYC 4162-665-1. There may be other planets lurking around it.
How likely is it that we will find a habitable Earth-like world? It's still a long shot. One of the best estimates puts the number of potentially habitable, terrestrial planets in our galaxy at 1 in 50. That would mean that there could be, conservatively, two such planets for every one of the 400 billion stars in the universe.
One of the most exciting new results of the planet-finding program is the possibility of finding a "super-Earth." These planets may be the final evolutionary step before they become suitable for life. Scientists estimate that these big Earths (between 2 and 3 times the size of our own) are common in the universe, and the TESS telescope will search for hundreds of them.
The fact that we don't yet know what life looks like (or if it could even survive on other planets) doesn't stop our science fiction-loving imagination from dreaming about extraterrestrial worlds.
For example, if we ever manage to send a spacecraft to another world (perhaps Tau Ceti in the not-too-distant future), it would take them several years to travel the 150 billion kilometers from Earth to this tiny star. Would we be willing to wait around for our astronauts to return? It's entirely possible. But the truth is, we're far more likely to find aliens on another planet than to visit them. And on these faraway worlds, who knows how long we'll be able to communicate with them or whether they'll be able to communicate with us?
While new and exciting exoplanet discoveries are being made around stars in our own neighborhood, that doesn't mean we can afford to stop looking for worlds beyond our own. It would be tragic if we missed a world that could be home to extraterrestrial life. We'd never know if it was there because we wouldn't be looking for it.
When Are We Going?
The nearest star to our sun is Proxima Centauri, which is a part of Alpha Centauri. Alpha Centauri is a triple-star system: Alpha Centauri A and Alpha Centauri B are the brighter stars, and Proxima Centauri is the fainter third member of the system.
Proxima Centauri is a red dwarf star like our sun, but it's smaller and cooler. It's 4.2 light-years away, which means that when we look up at the night sky and see this faint star, it's actually 4.2 years away. This fact, along with the brightness of Proxima Centauri, means that in our cosmic neighborhood—in our own solar system—we can see Proxima Centauri without our telescopes. If you were on Earth and you looked up into the sky at night (under very good conditions), you would see the stars Alpha Centauri and Proxima Centauri moving across the sky. It's the movement of these stars that tells us we're on a rotating planet.
This fact can make interstellar travel a little difficult, because stars in our own neighborhood don't orbit the center of the galaxy; they go back and forth along the galaxy's plane. This makes it difficult for us to imagine what it would be like to travel through space. While we might travel at 100,000 kilometers per hour toward Alpha Centauri and Proxima Centauri, Alpha Centauri would be moving away from us.
But it's not impossible to do this type of travel—it just requires a lot of hard work and a lot of fuel. For that reason, human beings might not travel to distant exoplanets just yet. However, because most stars in our galaxy are billions of light-years away from us, we don't have much choice but to send out probes or humans into space if we want to get to them.
So let's keep trying. It might take us a few hundred thousand years, but we will get there.
The Sun: We're Here
Although the sun is the brightest star in the sky, there's another—much dimmer—star that could overshadow it: Alpha Centauri B, a red dwarf star, which is not much larger or more massive than our own sun, but has a planet with three times the mass and 50 percent more diameter than Earth.
"It will be habitable for about 200 million years," says Steven Vogt, a professor of astronomy at UC Santa Cruz and the leader of a research team that identified the planet. (Vogt is one of the scientists who contributed to the discovery of Proxima b in 2016.) The only thing we don't know about this exoplanet is its mass—it's somewhere between three and 20 times the mass of the Earth. If it's similar to Earth, it would be roughly a quarter of Earth's size, so it would have a diameter similar to the size of Jupiter.
Since there's no solid ground under Alpha Centauri B, the planet would be covered in a thick, steamy atmosphere. The only thing that might be possible for life to survive on is a deep ocean, because at the surface it would be about 100 degrees Celsius (212 degrees Fahrenheit) and much hotter closer to the star. But this is still pretty warm for aliens. However, it's still possible that life could thrive on the ocean's floor, similar to the conditions of the Deep Impact mission. But we still don't know how much water is there.
According to Vogt's estimations, if we were to build a large space telescope—a telescope with a diameter equal to the distance between Earth and the sun—we would be able to see a quarter of the star with this huge telescope. If such a telescope were mounted on a spacecraft that traveled at a fraction of light speed, it would take 25,000 years to get there from our home planet.
The nearest star to our sun is Proxima Centauri, which is a part of Alpha Centauri. Alpha Centauri is a triple-star system: Alpha Centauri A and Alpha Centauri B are the brighter stars, and Proxima Centauri is the fainter third member of the system.
Proxima Centauri is a red dwarf star like our sun, but it's smaller and cooler. It's 4.2 light-years away, which means that when we look up at the night sky and see this faint star, it's actually 4.2 years away. This fact, along with the brightness of Proxima Centauri, means that in our cosmic neighborhood—in our own solar system—we can see Proxima Centauri without our telescopes. If you were on Earth and you looked up into the sky at night (under very good conditions), you would see
