Two potentially habitable planets discovered just 12 light years away

Astronomers have identified four Earth-sized planets orbiting a star 12 light years from our own Sun, two of which are in the habitable zone and so could be host to liquid water.

The planets, which are thought to be around 70% larger than Earth, orbit a star known as tau Ceti, which is in the Cetus constellation, and has a similar spectral range to our sun, although only 78% of the mass.

As a result, the astronomers, led by a team at the University of Hertfordshire, not only believe that the two within the habitable zone could be host to life, but could be targets for colonisation by our descendents.

The research, which is published today in the Astronomical Journal, represents a significant step in the ongoing hunt for life on other planets, providing one of the closest discoveries outside of our own solar system.

The Cetus constellation, which is traditionally depicted as a whale in mythology

The planets were detected not by direct imaging – that is, capturing an image of them using an instrument such as the Hubble space telescope – but by observing wobbles in the movement of the star, from which they can infer the existence, likely size and orbit distance of surrounding planets.

“We’re getting tantalisingly close to observing the correct limits required for detecting Earth-like planets,” said study lead author Dr Fabo Feng, a research fellow at the University of Hertfordshire.

“Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth’s habitability through comparison with these.”

This technique was first implemented by the astronomers in 2013, and has proved vital to the discovery of planetary bodies.

“We realised that we could see how the star’s activity differed at different wavelengths and use that information to separate this activity from signals of planets,” said Dr Mikko Tuomi, study co-author and pioneer of the technique.

“Since then we’ve painstakingly improved the sensitivity of our techniques and could rule out two of the signals our team identified in 2013 as planets. But no matter how we look at the star, there seems to be at least four rocky planets orbiting it.”

The planets orbiting tau Ceti, compared to those of Earth. The green band is the habitable zone, where planets are thought to have the potential to host life. Image courtesy of the University of Hertfordshire

However, while the discovery is undoubtedly exciting, the astronomers have identified another quality to the star that could make the survival of life, either in the form of biologically native organisms or occupying humans, more challenging.

Tau Ceti also have what the university describes as a “massive debris disc” surrounding it, which would likely mean that the planets would be frequently bombarded with asteroids and comets, playing havoc with any atmosphere are providing challenging environmental conditions.

Nevertheless, the planets could well prove to be a valuable stop for future humans, and may even provide a home for hitherto-undiscovered life.

The Moon may have far more water than previously thought: scientists

The Moon may be hiding vast deposits of water beneath its surface, according to the results of a study of lunar satellite data.

Scientists from Brown University studied data about the Moon’s volcanic deposits in a bid to learn more about the lunar interior – the mantle that sits below its surface. What they found contradicted long-held assumptions about the Moon’s interior, suggesting that it is rich in water, not dry as was previously assumed.

This supports the analysis of lunar samples from the Apollo 15 and 17 missions, which first cast doubt on the dry mantle theory. Among the samples brought back were volcanic glass beads, which have since been found to contain as much water as some rocks found on Earth.

The research, which is published today in Nature Geoscience, suggests that these samples were, in fact representative of the Moon as a whole, indicating it is far wetter than traditionally thought.

Volcanic glass beads brought back from the Moon during the Apollo 15 mission. Image courtesy of NASA. Above: a depiction of scan results from the Moon’s surface, showing abundant water deposits. Image courtesy of Milliken Lab / Brown University

“The key question is whether those Apollo samples represent the bulk conditions of the lunar interior or instead represent unusual or perhaps anomalous water-rich regions within an otherwise ‘dry’ mantle,” said Ralph Milliken, study lead author and an associate professor in Brown’s Department of Earth, Environmental and Planetary Sciences.

“By looking at the orbital data, we can examine the large pyroclastic deposits on the Moon that were never sampled by the Apollo or Luna missions.

“The fact that nearly all of them exhibit signatures of water suggests that the Apollo samples are not anomalous, so it may be that the bulk interior of the Moon is wet.”

The research was conducted using orbital spectrometers, which measure which wavelengths of light are reflected by a planet’s surface. By determining which wavelengths were absorbed and which were reflected, the scientists were able to determine the presence of specific compounds and minerals.

A design for a lunar base by Foster + Partners developed for the European Space Agency, one of many agencies looking to establish a base on the Moon that could benefit from the findings. Image courtesy of ESA/Fosters Partners

With considerable discussion of the establishment of a lunar base by numerous space organisations, the quantity of water on the planet is significant. Not only is it valuable in sustaining humans and supporting systems, but also can be used as the basis for rocket fuel.

“Other studies have suggested the presence of water ice in shadowed regions at the lunar poles, but the pyroclastic deposits are at locations that may be easier to access,” said study co-author Shuai Li, a former Brown PhD graduate and postdoctoral researcher at the University of Hawaii.

“Anything that helps save future lunar explorers from having to bring lots of water from home is a big step forward, and our results suggest a new alternative.”