Closest Star To Our Sun Beckons In New Hubble Image

Remember that planet discovered near Alpha Centauri almost exactly a year ago? As you may remember, it’s the closest system to Earth, making some people speculate about how quickly we could get a spacecraft in that general direction. Four light years is close in galactic terms, but it’s a little far away for the technology we have now — unless we wanted to wait a few tens thousands of years for the journey to complete.

Meanwhile, we can at least take pictures of that star system. The Hubble Space Telescope team has released a new picture of Alpha Centauri’s sister star, Proxima Centauri. While Proxima is technically the closest star to Earth, it’s too faint to be seen by the naked eye, which is not all that surprising given it is only an eighth of the sun’s mass. Sometimes, however, it gets a little brighter.

“Proxima is what is known as a ‘flare star’, meaning that convection processes within the star’s body make it prone to random and dramatic changes in brightness.” stated the Hubble European Space Agency Information Centre.

“The convection processes not only trigger brilliant bursts of starlight but, combined with other factors, mean that Proxima Centauri is in for a very long life.”

How long? Well, consider the following: the universe is about 13.8 billion years old and Proxima is expected to remain in middle age for another four TRILLION years. Plenty of time for us to send a spacecraft over there if we’re patient enough. (The universe itself is expected to last a while, as Wise Geek explains.)

The picture was nabbed with Hubble’s Wide Field and Planetary Camera 2, with neighbouring stars Alpha Centauri A and B out of the frame.

Source: Hubble European Space Agency Information Centre

Next Door Neighbors? Earth-Sized Planet Discovered in Nearest Star System to Us

Artist’s impression of the planet around Alpha Centauri B. Credit: ESO

Artist’s impression of the planet around Alpha Centauri B. Credit: ESO

Astronomers have discovered an enticing new planet that could be considered our next-door neighbor. The planet is orbiting a star in the Alpha Centauri system — the closest system to our own, just 4.3 light years away — and the planet has a mass about the same as Earth. It is also the lightest exoplanet ever discovered around a sun-like star. While this planet is likely too hot to contain life as we know it, the star system could possibly host other worlds that could be habitable, researchers from the European Southern Observatory at La Silla say.

“This result represents a major step towards the detection of Earth twins in the immediate vicinity of the Sun,” the team wrote in their paper.

“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,” said Stéphane Udry from the Geneva Observatory, a co-author of the paper that will be published in Nature on Oct. 17, and member of the team that used the HARPS instrument to find the planet. “But it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems.”

The planet is called Alpha Centauri Bb and it whips around its star every 3.2 days, orbiting at a distance of just 6 million kilometers (3.6 million miles), closer than Mercury’s orbit around the Sun. (Earth orbits at a comfortable 150 million kilometers (93 million miles) from the Sun.) So it is likely very hot and covered with molten rock, the researchers say.

Many astronomers have thought that the Alpha Centauri system would be a perfect candidate to host Earth-sized worlds. In fact, in 2008, a team of astronomers ran computer simulations of the system’s first 200 million years, and in each instance, despite different parameters, multiple terrestrial planets formed around the star. In every case, at least one planet turned up similar in size to the Earth, and in many cases this planet fell within the star’s habitable zone.

But while astronomers have looked for years, previous searches of planets in the Alpha Centauri system came up empty.

Until now.

“Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days,” says Xavier Dumusque (Geneva Observatory, Switzerland and Centro de Astrofisica da Universidade do Porto, Portugal), lead author of the paper. “It’s an extraordinary discovery and it has pushed our technique to the limit!”

The European team detected the planet by using the radial velocity method — by picking up the tiny wobbles in the motion of the star Alpha Centauri B created by the gravitational pull of the orbiting planet. The effect is extremely small, as it causes the star to move back and forth by no more than 51 centimeters per second (1.8 km/hour). The team said this is the highest precision ever achieved using this method.

Alpha Centauri is one of the brightest stars in the southern skies and is actually a triple star — a system consisting of two stars similar to the Sun orbiting close to each other, designated Alpha Centauri A and B, and a more distant and faint red component known as Proxima Centauri.

Alpha Centauri B is very similar to the Sun but slightly smaller and less bright. The orbit of Alpha Centauri A is hundreds of times further away from the planet, but it would still be a very brilliant object in the planet’s skies.

A wide-field view of the sky around Alpha Centauri was created from photographic images forming part of the Digitized Sky Survey 2. The star appears so big just because of the scattering of light by the telescope’s optics as well as in the photographic emulsion. Credit: ESO

The first exoplanet around a Sun-like star was found by the same team back in 1995 and there are now 843 Exoplanets with the addition of Alpha Centauri Bb. Most are much bigger than Earth, and many are as big as Jupiter. The previous closest exoplanet was Epsilon Eridani b, 10.4 light years away.

The challenge astronomers now face is to detect and characterize a planet of mass comparable to the Earth that is orbiting in the habitable zone around another star. The first step has now been taken, the team says.

“This result represents a major step,” said Dumusque. “We live in exciting times!”

So, how long would it take for us to get to this planet? Using current technology, our slowest mode of space transportation, ion drive propulsion, it would take 81,000 years. Using the speeds of one of the fastest spacecraft (Helios 2) and traveling at a constant speed of 240,000 km/hr, it would take about 19,000 years (or over 600 generations) to travel the 4.3 light years.

Read the team’s paper (PDF)

Source: ESO

Distance to Alpha Centauri

Alpha Centauri is the closest known star system to the Solar System. Also known as Rigil Kentaurus, Alpha Centauri is actually a multiple star system. It’s certainly a binary star, with two sunlike stars orbiting one another. And there’s also a red dwarf star, Proxima Centauri, which astronomers still argue about whether it’s part of the system.

The closest star in the group is Proxima Centauri, located only 4.243 light-years from the Sun. And then the Alpha Centauri AB stars are located 4.37 light-years away.

With the unaided eye, Alpha Centauri looks like a single star. But then under the power of a telescope, it’s possible to split them and see the individual stars separately. Alpha Centauri is only really prominent in the southern skies, and below the horizon to astronomers in the north.

Alpha Centauri A is slightly larger and more luminous than the Sun, while Alpha Centauri B is smaller and cooler than the Sun. But Proxima Centauri is a tiny red dwarf star, with only 1/8th the mass of the Sun.

We’ve written several articles about the Alpha Centauri system. Here’s an article about how we might be able to detect Earthlike planets around Alpha Centauri, and here’s an article about the sounds of Alpha Centauri.

Here’s a cool image of Alpha Centauri at Astronomy Picture of the Day.

We’ve also recorded an episode of Astronomy Cast about what it might take to travel to Alpha Centauri. Listen here, Episode 145: Interstellar Travel.

Why Haven’t Planets Been Detected Around Alpha Centauri?


Question: Why aren’t astronomers looking for planets around nearby stars like Alpha Centauri?
Answer: That’s a great question. Since Alpha Centauri is only a little over 4 light-years away, why aren’t astronomers studying it for planets, instead of the more distant stars.

Astronomers have included stars like Alpha Centauri in their search for extrasolar planets, they just haven’t found them yet. That’s because the techniques used to find extra solar planets require very large planets orbiting very close to their parent stars.

The first technique is called the radial velocity method. This is where the gravity of the planet yanks its parent star back and forth. The changes in the star’s velocity are measurable in the light that reaches the Earth.

The second technique looks for transits. This is where the planet passes in front of the parent star, dimming it slightly. By measuring the amount the light dims, astronomers are able to know if there’s a planet there, calculate its size and even determine what’s in its atmosphere.

A third technique detects microlensing events. A closer star focuses the light from a more distant star with its gravity. From Earth, we see a flare in brightness as the two stars line up perfectly. If the closer star has a planet orbiting it, that will change the light curve that astronomers detect, allowing them to calculate the size of the planet.

Most of the planets discovered to date are known as Hot Jupiters. These are planets much larger than Jupiter that orbit within the orbit of Mercury.

A team of astronomers led by Javiera Guedes from the University of California think that an Earth-sized planet should be detectable orbiting Alpha Centauri. They’re working to get a single dedicated telescope to watch the star, and work out if there are planets there. According to their calculations, it should only take about 5 years of intense observations by a dedicated telescope to work out the answer.