History was made when a team of astronomers based in Geneva recently discovered a new planet orbiting Alpha Centauri B, a star that is the galactic equivalent of a saunter from BLC to the library away from us. The new planet was — not too creatively — named Alpha Centauri Bb. This is not only the most recently discovered planet, but also the closest planet to our solar system ever discovered.
Alpha Centauri Bb presents astronomers with a unique opportunity to learn more about it because of its proximity to our solar system. “Alpha Centauri B is the closest star and there are science questions about how planets form, their compositions, and whether they are sustaining life … and the closer we are, the more likely we are to learn something,” Adam Riess, a professor and researcher at Hopkins and the winner of the 2011 Nobel Prize in Physics, said of the planet in an interview with The News-Letter. Furthermore, Alpha Centauri B is similar in mass and temperature to our sun, which means there may be a higher chance that this planet is similar to earth.
Our close proximity to Alpha Centauri Bb isn’t the only thing that makes this a monumental find. The planet is also one of the smallest discovered so far by astronomers. Its mass is only slightly higher than that of the earth. Almost all the planets that have been found up to this point were gas giants — closer to Jupiter in size and composition — or larger, rocky planets closer in size to Neptune or Uranus.
You may be wondering: how does one go about finding a planet orbiting a star more than four light-years away? Well, there are two ways.
The first is to look at the amount of radiation coming from a star and wait to see if there is a dip in the amount of radiation coming into your telescope. If there is a dip in radiation and this dip continues in a cyclic pattern, there is likely a planet orbiting the star in question.
The other way — the way that the team from Geneva used — is to look at the “wobble” of the star due to the gravitational pull
of the planet. As Newton taught us, for every action there is an equal and opposite reaction. This means that when a star’s gravity pulls on a planet, the planet pulls back. This causes the star to “wobble” at a very slow rate called “radial velocity” and this can sometimes be observed by our telescopes. The new planet was observed to cause a radial velocity of 50 cm/s in Alpha Centauri B, the equivalent of a leisurely stroll. The accuracy required to measure such a slow velocity over four light-years away is amazing.
The real question that everyone is asking is whether there is life on this planet. Unfortunately, there is hardly any chance that Alpha Centauri Bb sustains life. Its orbit puts it very close to its star, well outside of the so-called habitable or “Goldilocks” zone where water can remain in liquid form. The temperature on the surface is estimated to be around 1200 degrees Celsius.
So what are the implications of finding a new rock orbiting a star? It’s important because small planets like Alpha Centauri are often formed in multi-planet systems. This means that there may be other planets orbiting Alpha Centauri, planets that may lie in the star’s habitable zone.
If other planets orbiting Alpha Centauri B are discovered, we will first want to learn about their atmospheres. Scientists will want to know if the planet has water on its surface and if its composition is similar to Earth’s. To do this, astronomers will use spectroscopy to look at the tiny sliver of atmosphere visible around the planet when it passes in front of the star.
In a recent talk at the Space Telescope Science Institute, renowned planet-finder David Charbonneau discussed a statistical analysis done by one of his graduate students at Harvard University. The study revealed that there is a 95 percent chance an earth mass planet with liquid water exists in the habitable zone of a star within 23 parsecs (75 light-years) of Earth. This number is very encouraging. We are well on our way to finding life out there.