It can seem like the field of science is limited to torturous problem sets in the SciLi dungeon basement. But there is awesome stuff going on in the sciences at Brown and beyond, though it can be difficult to find when you’re wasting away in the library. BlogDH presents “Science Beyond the SciLi”; so even if you’re reading this inside those concrete walls, you can see a glimmer of scientific hope.
Science isn’t a mystery novel, so here’s the punch line: we are probably not alone. There are most likely other life forms out there wondering if they are alone in the universe. Makes your midterms feel a little less important, doesn’t it?
Now, let’s back up a second. How can I make this crazy claim? Well, I went to the inaugural lecture of the Presidential Colloquium Series ThinkingOut Loud: DECIPHERING MYSTERIES OF OUR WORLD AND BEYOND (the formatting of the title might be the biggest mystery of them all). President Paxson introduced the speaker (hence “Presidential Colloquium”), John Johnson, a professor of astronomy at the Harvard-Smithsonian Center for Astrophysics, who lectured on “Searching For Life Basking in the Warmth of Other Suns.”
Johnson’s job is to search for life on other planets. But he doesn’t just sit around basking in sunlight while sending signals to aliens and waiting for them to respond (although we have done that). He researches exoplanets, planets that orbit stars other than our own sun. A stellar astrophysicist by day and a planet hunter by night, Johnson finds undiscovered exoplanets and characterizes them, looking for planets that are not too hot and not too cold—ones that might be just right to harbor life.
As Carl Sagan described, a galaxy is made up of “billions upon billions” of stars. The goal of exoplanetary science is to provide a galactic context for planets, rather than just studying our own. Putting together a theory of exoplanets based on our observations of Earth is like “doing a sociology study with only yourself as the subject,” in Johnson’s words: it’s nearly impossible to prove or disprove anything.
So how do we discover these exoplanets? One way is to track the movement of the stars they orbit. Actually, that’s a lie. Planets don’t orbit stars: planets and stars orbit each other’s center of mass. A planet, though tiny compared to its star, tugs slightly on the star as it orbits it; as you might have learned in high school physics, for every action there is an equal and opposite reaction. So even though we may not be able to see the planet, we can detect its effect on its star.
Another way to find planets is to catch them eclipsing their stars, just as the moon can eclipse our sun. If we see a periodic dip in a star’s brightness, we can deduce that a planet is passing in front of it as it orbits.
In order to apply these planet-hunting techniques, we need a telescope. A big telescope. Johnson uses the Keck Telescope in Hawaii, a 10-meter optical telescope that has a large aperture to let in lots of light, as more light means you can measure more stars. The telescope has monitored more than 3,000 stars over 15 years, leading to the discovery of many exoplanets. This may not seem like an incredible number compared to the billions and billions of stars in our galaxy, but tracking stars is tricky, in large part because we are on this moving platform known as Earth.
From these and other observations, we know that the majority of stars in our galaxy are red dwarves, smaller and relatively cool stars. These are ideal for planet-hunting, because the star-to-planet size ratio is smaller, making it easier to detect planetary eclipses.
Using his big telescope and the techniques described, Johnson discovered a planet. But as he and his team tracked it, they noticed something odd: the planet completed a rotation around its star in 4.2 days. That means its year is only 4.2 days long. As Johnson noted, it’s “not a great place to pay your taxes.” They also found that the planet is very hot and gaseous, like Jupiter, hence the creative name “hot Jupiter.”
For each of the planets that Johnson and other astronomers have discovered, there are many more out there. He describes it like cockroaches: you see one, and you know a bunch more are lurking just out of sight. By extrapolating from the planets we have discovered, we know that half of all planets are in multiple planet systems like our own, with an average of six planets per star, while the other half are singletons.
We also know that planets of a similar size as Earth are by far the most common. If you do the math, you’ll find that there are 0.56 Earth-sized planets per red dwarf star. This means if you have any two red dwarves, you can bet that one of them hosts a habitable-zone planet. And that planet may host life.
But how can we figure out whether there are actually critters living on these planets, basking in the warmth of their own suns? One way is to use the very same telescopes that found the planets. Some of the light from the star that the telescope collects has to pass through the planet’s atmosphere, and, using spectroscopy, we can figure out the chemical makeup of the atmosphere. This could allow us to detect biosignatures—signs of life. For example, bacteria could be expelling methane that would result in a higher level of gas than expected. Or maybe we would even detect pollution in the atmosphere caused by other intelligent life—thanks for something, climate change!
Astronomers have also tried sending radio signals out into space in the hopes that they will one day be received by other intelligent life. This is great in theory, but due to the cosmic speed limit—the speed of light—that signal is probably still on its way, and we will have to wait hundreds of years for a response, even if it is received. But from Johnson’s research and that of other planet-hunting astrophysicists, there is strong evidence that there could be other life out there—that we are not alone in this awesome (in the very literal sense of the word) Universe.
While you wait for aliens to contact us, check back for more Science Beyond the SciLi!