Just like home, 100 million light years away: more earthsized extra-solar planets discovered than ever before
If life exists elsewhere in the universe, how come we haven’t seen other beings yet? UC Berkeley astronomer Dr. Geoff Marcy addressed this and other questions in our latest enrichment talk at the Chabot Space and Science Center.
First, Dr. Marcy discussed NASA’s Kepler observatory, which suggests many more earth-like planets exist than we’d previously thought. He treated us to a video of Kepler’s 2009 launch from the Kennedy rocket, complete with audience yelling and wonderment.
Astronomers often find exoplanets, planets outside our solar system, by watching them pass in front of the stars they orbit. Kepler captures a snapshot of space every minute, and thanks to its ultra-stability, can detect a star’s becoming one ten-thousandth less bright. Regular variability in stellar brightness suggests the presence of a planet, and Kepler’s powerful enough to detect something just forty percent larger than Earth.
And, according to equations discovered and developed by the astronomer Kepler, if we know how long it takes for a planet to rotate around its star, then we can figure out how far away it is from the star. This gives us some clue about how much light it receives and its temperature.
After astronomers locate an exoplanet, they can follow up using the Keck telescope array in Hawaii. The star’s stellar wobble, its reflex motion in response to being orbited, is called the Doppler shift. This arises from the Doppler effect, where the wavelengths of light and sound change slightly as an object moves, either toward or away from the observer. Scientists can calculate the mass and density of the planet from this Doppler shift.
Dr. Marcy showed a chart of all planets the Kepler craft has found, plotted by distance from their stars and size. A great number of them ranged from 1-4 times Earth’s size, with dozens roughly the size of Earth. After adding to the total to figure in planets which Kepler likely missed because their orbits were tilted relative to its area of view, astronomers estimate that 23% of all sunlike stars have planets 1-3 times as far away as Earth.
Researchers, such as Harvard’s Courtney Dressing, are trying to find out how many of these earthlike planets might receive the same amount of sunlight as we do. One recently located exoplanet seems to have a similar temperature and orbital period (days spent orbiting its star) as Earth. These conditions place it within the theoretically habitable zone for life as we understand it.
If we shrunk the Milky Way to the size of the United States, the nearest possibly habitable planet would be just across the Golden Gate Bridge! In actuality, it’s just ten light-years away, not that long on a galactic scale.
Most stars are red dwarves, the smallest type of star, and researchers estimate that 15% of red dwarves host Earthlike planets. Kepler alone has located over 400 multiplanet systems.
This, naturally, leads to speculation about whether all these potentially habitable planets could host intelligent life. After all, a galaxy containing 200 billion stars could have around 100 billion planetary systems, with 10 billion of those habitable.
‘So, where is everyone?’ Dr. Marcy asked. As a response, he speculated that nearby civilizations could have grown up and developed, then blown themselves up before Earth life arose, by perpetrating nuclear war or climate change. Or, the life forms never evolved intelligence or self-awareness, as it never conferred a significant survival advantage. Dr. Marcy looked at the dinosaurs as an example, as some had larger brains than others, but these seemed no more likely to survive and reproduce than the others.
It could simply be that life and civilizations are dispersed throughout the universe, and the nearest alien city is far away from us, given our space travel and observation capabilities.
Regardless of why we’re still waiting on an encounter with alien life forms, Dr. Geoff Marcy gave our imaginations and curiosity fertile ground to play with in this talk. Not only is there so much out there in space, as the lead character’s father says in the movie Contact, but there’s so much more out there than we thought that looks and works like our own corner of the universe.