Too hot? Too cold? Searching for a 'Goldilocks' zone
By Amanda Jermyn

The recently retired Kepler space mission detected just under 6,000 possible planets and discovered over 2,600 confirmed planets, all within a small patch of our Milky Way galaxy. From this we can infer that our galaxy alone should contain billions of planets, of which some 10 billion could potentially be habitable. And even within our own solar system, the planet Mars and some of Saturn’s and Jupiter’s moons have been identified as places that might harbor life. So now a myriad of possible targets await us in the search for life beyond planet earth.

With so many places to look for alien life, one way to narrow down the search is by identifying planets with earthlike properties. Life as we know it requires liquid water and thrives on a small rocky planet. So astronomers search for rocky planets somewhere between half and twice the size of earth that orbit their stars within the habitable or “Goldilocks” zone. This is the range of distance from a star where the temperature is not too hot and not too cold, in other words, just right for liquid water to exist. Depending on the type of star, the habitable zone for planets could be different from that in our own solar system. Red dwarf stars are much cooler than our sun, so their habitable zones are closer to the star than ours.

Our search for life should also focus on planets with uniform orbits: Planets with erratic orbits might become too hot when they veer close to their star and too cold when they orbit farther away.

Some planets are so close to their stars that their orbits are tidally locked, meaning that the star’s gravitational pull makes one side of the planet always face the star while the other side is always in darkness, just like our moon. Until recently such planets were considered poor candidates for life because one side would always be too hot and the other always too cold. However, current modeling and observations suggest that winds circling these planets might help moderate their temperatures.

Any planet conducive to life would also require a magnetic field to shield life from harmful radiation.

Another important factor in establishing if a planet is habitable is whether it has an atmosphere, and if so, what kind. Six key elements are thought to be essential for the kind of life we have on Earth: carbon, oxygen, nitrogen, hydrogen, sulfur and phosphorus, so any search for life would attempt to detect their presence. Recently, for the first time, an atmosphere with water and methane, a potential indicator of life, was detected on an earthlike planet beyond our solar system.

Even here on earth life takes many strange forms and thrives in environments once thought inhospitable, such as deep sea hydrothermal vents, in a lake under Antarctic ice, and in the far depths of a gold mine. In Mono Lake in California bacteria have been trained to live on a diet of arsenic, and we’ve discovered microbes that dine on electrons from rocks. Given the diversity of life here on earth, how different might it be elsewhere in the universe, and if it exists, would we even recognize it as such?

Finding life elsewhere would be a game-changer. We would discover that we are not alone in the universe, that life is not unique to our planet, and perhaps be dazzled by the strange forms it might take. Stay tuned for more on the search for life in next month’s column.

Join the Springfield Stars Club on Tuesday, March 26th at 7pm at the Springfield Science Museum for a talk by Paul Cardone on “New Mexico Nights Observatory.” Cardone is an amateur astronomer and telescope maker who is active in astronomy outreach locally. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.

Also, on Friday, April 5th at 7:30pm, the Stars Club and the Springfield Science Museum will host “Stars over Springfield,” an astronomy adventure for the whole family. Marguerite Seuffert and Crystal Mengele will present “Stars Game Night,” an astronomy quiz show with audience participation.