Astronomers Discover Alien Planet In Our Milky Way : The Two-Way : NPR

Astronomers Discover Alien Planet In Our Milky Way : The Two-Way : NPR

We really do live in a time of unprecedented scientific discovery, and it is positively invigorating! Like goosebumps all over and tingles and butterflies in the stomach exhilarating. The limits of our knowledge and understanding of the Universe seems to be expanding in similar fashion to the very accelerating expansion of the Universe itself! And, equally exciting is the fact that there is so much that we don't know, that remains to be discovered and explained.

In roughly the past 10 years, scientists have discovered more than 500 planets located in parts of the Milky Way galaxy outside our Solar System. Such planets are called exoplanets. See, e.g., http://en.wikipedia.org/wiki/Extrasolar_planet. Now, scientists have discovered an extragalactic exoplanet--a planet of extragalactic origin (it entered the Milky Way from a different galaxy altogether). According to the scientists in this piece on NPR, around six to nine billion years ago the Milky Way swallowed up a dwarf galaxy. This recently-discovered extragalactic exoplanet and its star, called HIP 13044, are what is left over from that cosmic merger of galaxies.

Dr. Robert Massey of the UK's Royal Astronomical Society notes the significance of this discovery: It provides the first hard evidence of a planet of extragalactic origin. Put another way, it is evidence that planets exist not just in the Milky Way. Planets may -- very probably do -- exist in galaxies throughout the Universe. Quite possibly ALL galaxies throughout the Universe. Can you grasp the profundity of that?

Let's do some simple math. Maybe that might help you get your mind around that profound significance, that which should render one flat dumbstruck with awe.

Let's assume the Milky Way is an average galaxy. The Milky Way is 100,000 light years across and is estimated to contain somewhere between 200 and 400 billion stars. Let's say 300 billion, or 3 x 10^12 (read "three times ten to the twelfth power"). Our Sun is one of those stars, and it has 8 planets in its solar system (yes, 8, because Pluto has been demoted from planet status because it does not meet the criteria for planet classification developed in 2006 by the International Astronomical Union. Dr. Neil DeGrasse Tyson, a member of the IAU and director of the American Museum of Natural History's Hayden Planetarium, recently had a very entertaining and educational special on PBS about his role in demoting Pluto to dwarf planet status). Observations strongly indicate that another solar system in the Milky Way containing the star, Gliese 581, contains at least 6 planets. See http://en.wikipedia.org/wiki/Gliese_581. Let's crudely estimate that, on average throughout the Milky Way, there are two planets around each star. That gives us an estimate of 600 billion (6 x 10^12) planets in the Milky Way. With me so far? Don't tune out yet.

Now, there are an estimated 200 billion (2 x 10^12) galaxies in the "visible" Universe. See http://www.universetoday.com/30305/how-many-galaxies-in-the-universe/. I say visible because a whole part of the Universe is expanding away from us faster than the speed of light (yes, that's possible. Google some of the works of Stephen Hawking and Lawrence Krauss to understand why). Consequently, it is impossible for us ever to see that part of the Universe. Assuming that those 200 billion galaxies in the part of the Universe that is visible to us are, on average, like the Milky Way, then the total number of planets in the visible Universe is 600 billion multiplied by 200 billion. Sounds big, right? How big is that number? It's 12 x 10^24. That's a 12 with 24 zeros, which looks like this: 12,000,000,000,000,000,000,000,000. That's so big, we don't have a name for it. We refer to it simply as 12 times ten to the 24.

Even if this number is off by a factor of 100,000, we're talking about the possibility of the number of planets being in the neighborhood of 1 x 10^18, which is still incomprehensibly large. To give you an idea of the bigness of that number, think of it this way: If all the lotteries that have ever been played across the world were combined, your odds of winning would be really small. Impossibly small, right? Inconceivably small (think Vicini, the little Sicilian guy in The Princess Bride). The bigness of 12 x 10^24 is bigger in its bigness than the odds of all of those combined lotteries is small in its smallness (I haven't actually done that calculation, but I think that's right).

The profound, philosophical aspect of a Universe that very well may contain 1 x 10^18 to 1 x 10^24 planets is that the probability asymptotes infinitely close to 100% that billions or trillions or even crazier big numbers of these planets exist in the "habitable zones" around their respective stars and are rocky planets similar to Earth (as opposed to gas giants like Saturn, Jupiter, Uranus and Neptune where life is not possible). Earth is in our Sun's habitable zone: It lies not too close to the Sun where water would vaporize and remain in vapor form or dissipate into space; it lies not too far from the Sun where water would remain constantly frozen. It's also called the "Goldilocks Zone" because conditions are juuuuuust right for the existence of liquid water. As far as we understand life, it exists because of the presence of liquid water. So, the odds are literally astronomically high -- close to 100%, in fact, based on the mathematics -- that there are gajillions of Earth-like planets in Goldilocks Zones throughout the Universe where conditions for life exist. The discovery of exoplanets and extragalactic exoplanets, combined with some rudimentary arithmetic and the observations of the Universe scientists have been able to make because of the Hubble telescope and other instruments, enables us to offer an answer to that most profound philosophical question which humans across cultures have asked and wondered about for thousands of years, "Are we alone in the Universe?" It is almost 100% certainly, No.