Earth From Afar Would Look Only 82% Right For Life

From Lunar orbit, Earth is obviously habitable. But from a distant point in the galaxy, not so much. Image: NASA/LRO.

Right now, we’re staring hard at a small section of the sky, to see if we can detect any planets that may be habitable. The Kepler Spacecraft is focused on a tiny patch of sky in our Milky Way galaxy, hoping to detect planets as they transit in front of their stars. But if alien astronomers are doing the same, and detect Earth transiting in front of the Sun, how habitable would Earth appear?

You might think, because, well, here we are, that the Earth would look 100% habitable from a distant location. But that’s not the case. According to a paper from Rory Barnes and his colleagues at the University of Washington-based Virtual Planetary Laboratory, from a distant point in the galaxy, the probability of Earth being habitable might be only 82%.

Barnes and his team came up with the 82% number when they worked to create a “habitability index for transiting planets,” that seeks to rank the habitability of planets based on factors like the distance from its star, the size of the planet, the nature of the star, and the behaviour of other planets in the system.

The search for habitable exo-planets is dominated by the idea of the circumstellar habitable zone—or Goldilocks Zone—a region of space where an orbiting planet is not too close to its star to boil away all the water, and not so far away that the water is all frozen. This isn’t a fixed distance; it depends on the type and size of the star. With an enormous, hot star, the Goldilocks Zone would be much further away than Earth is from the Sun, and vice-versa for a smaller, cooler star. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” says Barnes.

Kepler has already confirmed the existence of over 1,000 exo-planets, with over 4,700 total candidate planets. And Kepler is still in operation. When it comes time to examine these planets more closely, with the James Webb Space Telescope and other instruments, where  do we start? We needed a way to rank planets for further study. Enter Barnes and his team, and their habitability index.

To rank candidates for further study, Barnes focused on not just the distance between the planet and the host star, but on the overall energy equilibrium. That takes into account not just the energy received by the planet, but the planet’s albedo—how much energy it reflects back into space. In terms of  being warm enough for life, a high-albedo planet can tolerate being closer to its star, whereas a low-albedo planet can tolerate a greater distance. This equilibrium is affected in turn by the eccentricity of the planet’s orbit.

The habitability index created by Barnes—and his colleagues Victoria Meadows and Nicole Evans—is a way to enter data, including a planet’s albedo and its distance from its host star, and get a number representing the planet’s probability of being habitable. “Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said Barnes, “so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”

So where does the Earth fit into all this? If alien astronomers are creating their own probability index, at 82%, Earth is a good candidate. Maybe they’re already studying us more closely.

 

The post Earth From Afar Would Look Only 82% Right For Life appeared first on Universe Today.

Spinning Worlds: Orrery of Kepler’s Exoplanets, Part IV

The past few years, Daniel Fabrycky from the Kepler spacecraft science team has put together some terrific orrery-type visualization of all the multiple-planet systems discovered by the Kepler spacecraft. An orrery, as you probably know, is a a mechanical model of a solar system, and the metal or plastic ones available these days usually show […]

Radio waves absent from the reputed megastructure-encompassed Kepler star?

Astronomers at the SETI institute (search for extraterrestrial intelligence) have reported their findings after monitoring the reputed megastructure-encompassed star KIC 8462852.  No significant radio signals were detected in observations carried out from the Allen Telescope Array between October 15-30th (nearly 12 hours each day).  However, there are caveats, namely that the sensitivity and frequency range were limited, and […]

What’s Orbiting KIC 8462852 – Shattered Comet or Alien Megastructure?

“Bizarre.” “Interesting.” “Giant transit”.  That were the reactions of Planet Hunters project volunteers when they got their first look at the light curve of the otherwise normal sun-like star KIC 8462852. Of the more than 150,000 stars under constant observation during the four years of NASA’s primary Kepler Mission (2009-2013), this one stands alone for the inexplicable dips in its […]

More livable than Earth? New index sizes up the habitability of alien exoplanets

Researchers at the University of Washington’s Virtual Planetary Laboratory have devised a new habitability index for judging how suitable alien planets might be for life, and the top prospects on their list are an Earthlike world called Kepler-442b and a yet-to-be confirmed planet known as KOI 3456.02. Those worlds both score higher than our own planet on the index: 0.955 […]

A Place for Alien Life? Kepler Mission Discovers Earth’s Older Cousin, Kepler-452b

Scientists say NASA’s Kepler Space Telescope has discovered Earth’s “older, bigger first cousin” –  a planet that’s about 60 percent bigger than Earth, circling a sunlike star in an orbit that could sustain liquid water and perhaps life. (…)Read the rest of A Place for Alien Life? Kepler Mission Discovers Earth’s Older Cousin, Kepler-452b (686 words) […]

Everything About Kepler-432b is Extreme, Especially the Way it’s Going to Die

Astronomers are calling Kepler-432b a ‘maverick’ planet because everything about this newly found exoplanet is an extreme, and is unlike anything we’ve found before. This is a giant, dense planet orbiting a red giant star, and the planet has enormous temperature swings throughout its year. In addition to all these extremes, there’s another reason you […]

Oldest Planetary System Discovered, Improving the Chances for Intelligent Life Everywhere

Using data from the Kepler space telescope, an international group of astronomers has discovered the oldest known planetary system in the galaxy – an 11 billion-year-old system of five rocky planets that are all smaller than Earth. The team says this discovery suggests that Earth-size planets have formed throughout most of the Universe’s 13.8-billion-year history, […]

Gallery: Some Of Kepler’s Strange New Worlds Outside The Solar System

With the latest Kepler space telescope exoplanet finding announced yesterday, the mighty planet hunter has now found 1,000 confirmed worlds — with about 3,000 more planetary candidates just waiting for confirmation. The NASA observatory has found exoplanets of many sizes — smaller than Mercury, the size of our Moon, the size of Jupiter or larger, […]

New Finds From Kepler: 8 New Worlds Discovered in the Habitable Zone

A fascinating set of finds was announced today at the 225th meeting of the American Astronomical Society (AAS), currently underway this week in Seattle, Washington. A team of astronomers announced the discovery of eight new planets potentially orbiting their host stars in their respective habitable zones. Also dubbed the ‘Goldilocks Zone,’ this is the distance […]