How Do Astronomers Find Exoplanets?

Artist's conception of exoplanet Kepler-16b. Image courtesy NASA/JPL-Caltech/R. Hurt.
Artist’s conception of exoplanet Kepler-16b. Image courtesy NASA/JPL-Caltech/R. Hurt.

By: Sara Knight
BU News Service

Last month astronomer Erik Petigura announced it was likely that our galaxy may have up to 40 billion Earth-like, habitable exoplanets swirling around their Sun-like stars. Petigura’s conclusion, which resulted from his analysis of Kepler satellite data, marks a huge milestone in the search for exoplanets – a field that has experienced a rapid expansion in the past decade. The ultimate goal of this extra-solar quest – to find planets with conditions able to support life as we know it – is only attainable if researchers can not only locate these other worlds, but discern their composition. Given that the nearest exoplanet is 4.37 light-years, or 26.22 trillion miles, away from Earth, it is no simple task. So how do researchers find and analyze alien worlds?

It comes down to tenacious observation and a lot of math. First, astronomers must set a satellite or telescope to record a given patch of space – for example, the Kepler satellite focuses on an astral window of about 100,000 stars. Then they wait for minute fluctuations in the amount of light a star gives off, which indicates a body, maybe a planet, passing in front of the star. Researchers confirm the light-blocking object as an exoplanet only after noting that the light fluctuates in a regular pattern, which can take years depending on the length of the planet’s orbit.

Once the light-blocker is verified as a planet the researchers ascertain its volume and mass. Luckily for them, finding the planet’s volume is relatively straight-forward – the amount the star’s light dims as the planet passes by denotes its size. Finding the planet’s mass is trickier: researchers must determine the strength of the gravitational attraction between the planet and star. The larger the attraction, the more massive the planet. The star itself is also “in orbit” around the center of mass between itself and the planet – it is just so massive that its orbit is more of a wobble than a proper ellipse. As the star wobbles, the frequency of its light changes in the visible spectrum – a phenomenon known as the Doppler effect. By observing these fluctuations, astronomers can figure out how much a star wobbles, and therefore the mass of its orbiting planet.

Artist's conception of exoplanets in the Milky Way. Image courtesy Wikimedia Commons.
Artist’s conception of exoplanets in the Milky Way. Image courtesy Wikimedia Commons.
After obtaining the figures for the planet’s volume and mass, finding the planet’s density is as simple as dividing the mass by the volume. Once astronomers figure out the density, they can extrapolate the sorts of materials that may make up the world. For example, an exoplanet with an extremely high density is probably composed of heavier materials, like rocks and metals.

In 2010, astronomers began using light frequency analysis not only to find the mass of the exoplanet, but also to infer its atmospheric makeup. While the planet passes between the star and their observation point, the chemicals in its atmosphere will give faint light signatures, which astronomers analyze using a chemical spectroscope. By noting which elements shift in the star’s chemical lineup when the planet passes by, they can infer the chemicals present in the exoplanet’s atmosphere.

So far, astronomers have found a huge variety of alien planets – some made mostly of metal and with 20 Earth-hour years, others made mostly of super-hot gas and that have silicate glass particles as rainfall. While the exoplanets with what we on Earth would consider extreme conditions are the coolest to read about, the ones that are able to sustain liquid water most interest astronomers. Those relatively ho-hum planets reside in the habitable zones of their stars – zones that astronomers believe life as we know it in our solar system may exist. And despite the report that there are probably 40 billion of them out there, we have only spotted twelve of them so far. But by remembering the scope of our search this humble figure seems a little less discouraging. After all, we can only focus on a small fraction of space at a time and stars are oriented randomly throughout the Universe – who knows what we’re missing?

One-Way Ticket to Mars

By Poncie Rutsch
BU News Service

It’s official: applications for the esteemed colonial voyage to Mars are now competitive. And your chances of getting picked are worse than your chances at getting into every Ivy League college…and also slightly worse than getting struck by lighting in your lifetime.

That’s right. Last year, Dutch entrepreneur Bas Lansdorp announced his plan to set up a colony on Mars by 2023. This year, they’re picking a total of 24 people to spend the next ten years training for said journey.

Four people from those 24 will embark on a seven-month journey in 2022. They’ll arrive at Mars in 2023, land in a small vehicle and leave the brunt of their ship in space (too heavy to land). They’ll live in inflatable dwellings with some air and food supplies sent over in advance.

Lansdorp and company will choose location of the settlement based on how much ice there is in the soil. They’ll melt this ice for water and break it apart via electrolysis for oxygen to breathe.

Of course, the documentation starts once Lansdorp and his team start training these 24 people. Reality TV show, 24/7/365. Of course, it won’t exactly be “live” since the delay between Mars and earth is anywhere from 3 to 22 minutes. Supposedly, this TV publicity will pay for most of the funding.

Regarding that 22-minute delay, that means if any sort of emergency takes place, Houston won’t know there’s a problem for 22 minutes. Sending help (via rocketship, of course) will take six months.

Oh yeah, but once you go, you can’t come back. Also, no skyping or phone calls. Only emails, texts, and the occasional video voicemail. Mind you, the delay would make a live conversation a little ridiculous.

Honestly, I don’t understand how 200,000 people have signed up. It’s one thing to go to space but it’s another to go to space and never return. It’s giving up everyone you’ve ever known. But then again, people hide out in Antarctica all the time, so I’m just the wrong demographic.

Mars One thought about this:

“However, there are individuals for whom traveling to Mars has been a dream for their entire life. They relish the challenge. Not unlike the ancient Chinese, Micronesians, and untold Africans, the Vikings and famed explorers of Old World Europe, who left everything behind to spend the majority of their lives at sea, a one-way mission to Mars is about exploring a new world and the opportunity to conduct the most revolutionary research ever conceived, to build a new home for humans on another planet.”

The deeper question throughout all this though is why do we do it? Do we do it to learn, or are we just doing it because we can?

Space research is important, but in order to research, we don’t necessarily have to go there ourselves. The Mars rovers have shown tremendous success – and we don’t have to feed them on the other side.

Perhaps someday it will be critical to repopulate Mars; when we destroy our own planet, for example. But until then, this seems like a classic case of science because we can…and really expensive science because we can, at that.

Needless to say, I’ll be glued to the live stream.

Mars road map of the future. Photo courtesy of Flickr Creative Commons user Bruce Irving.
Mars road map of the future. Photo courtesy of Flickr Creative Commons user Bruce Irving.