Tilted orbits
April 16, 2014

Astronomers Discover That Life Could Exist On Planets With Fluctuating Orbital Tilt

redOrbit Staff & Wire Reports - Your Universe Online

While experts have long believed that life could not exist on planets with a fluctuating tilt in their orbits, new research appearing in the April issue of the journal Astrobiology suggests that such obliquity variations could actually increase the planetary habitability in those worlds.

According to Weber State University physics professor John Armstrong, University of Washington astronomer Rory Barnes and their colleagues, these so-called “tilt-a-worlds” are less likely than fixed-spin planets to freeze over, since the heat from their host star is more evenly distributed throughout the planet’s surface.

This occurs only at the outer edge of a star’s habitable zone, which is the region of space around that star where rocky planets could maintain liquid surface water, the study authors added. Beyond that, planets enter a “snowball state” of global ice which makes life impossible.

The study results would expand the size of these perceived habitable zones by as much as 20 percent, in turn significantly increasing the number of worlds that could potentially be suitable for the existence of life. These so-called tilt-a-worlds would be potentially habitable because the orbital spin would cause the poles to point towards the host star from time to time, causing the ice caps to rapidly melt.

“Without this sort of ‘home base’ for ice, global glaciation is more difficult. So the rapid tilting of an exoplanet actually increases the likelihood that there might be liquid water on a planet’s surface,” Barnes, who was second author on the paper, said in a statement Tuesday.

Experts from NASA’s Goddard Space Flight Center were also involved in the study, which was funded by a grant from the US space agency’s Astrobiology Institute.

While Earth and the other planets in our solar system occupy essentially the same plane in space, Barnes said there is evidence of systems whose planets ride along at angles to each other. This means they can pull on one another from above or below, changing the direction of the planets’ poles in comparison to the host star.

The study authors set out to determine how an Earth-like planet would react if it had neighbors with off-kilter planetary alignments by using computer simulations. Furthermore, their research contradicts the longstanding view among the scientific community that planets require a large moon in order to potentially house life.

“We’re finding that planets don’t have to have a stable tilt to be habitable,” Barnes said, noting that even without the moon, Earth’s 23.5 degree tilt would increase by approximately 10 degrees. That would lead to climate fluctuation, but it would not make it impossible for life to exist on the planet.

Based on his team’s work, Armstrong said that the expansion of the habitable zone could nearly double the number of potentially habitable planets in the galaxy. If the larger region was applied to our solar system, he said that it would be possible for Earth to move beyond the orbit of Mars and still be habitable for at least part of the time.