Astronomers have found new evidence of the existence of an earthlike planet that lies a comparative stone&’s throw from our solar system. The discovery of GJ 581d was heralded in 2007 but new research last year cast doubt on the claims, saying data used to find it was probably just misinterpreted signals from stars. Astronomers had used a spectrometer to spot the planet, which measures “wobbles” in the wavelength of light emitted by a star caused as a planet orbits it. GJ 581d was said to be a super-earth with a mass seven times that of our own planet orbiting a red dwarf star that could also support up to four other planets. It was believed to be in the habitable “Goldilocks zone” in its solar system, where it is neither too hot nor too cold for liquid water to exist and support life on the surface.

Researchers revisiting the evidence claimed the body was actually just “stellar activity masquerading as planets” and its existence was widely dismissed without further questioning. But now astronomers from Queen Mary University, in London, and the University of Hertfordshire have claimed the statistical techniques used to discount GJ 581d is “inadequate” for planets of its small size.

Dr Guillem Anglada-Escudé, lead author of the paper published in Science, said, “The existence (or not) of GJ 581d is significant because it was the first earth-like planet discovered in the ‘Goldilocks’-zone around another star and it is a benchmark case for the Doppler technique. There are always discussions among scientists about the ways we interpret data but I’m confident that GJ 581d has been in orbit around (its star) Gliese 581 all along.” If GJ 581d does exist, it could be one of the most earth-like planets yet discovered as ranked by the Earth Similarity Index but that does not mean its surface is the same. For astronomers, the most exciting aspect is its relative proximity – 20 light years away in a galaxy that is 100,000 light years wide.

Lizzie Dearden/The Independent

Oldest Homo remains

A fossilised mandible and teeth from an ancient hominin has been found in Ethiopia and may be one of the earliest specimens of the genus Homo. The fossil, described in a paper in Science on 4 March, is estimated to be between 2.8 million and 2.75 million years old and exhibits a combination of Homo characteristics and those of the more primitive hominin genus, Australopithecus.

“It is a remarkable new fossil discovery from a really poorly understood timeframe in human evolutionary history,” said biological anthropologist Darryl de Ruiter of Texas A&M University who was not involved in the research. Until now, he added, “the earliest really reliable fossil evidence we had for the appearance of Homo was about 2 million years old”.

However, the fossil record for the earliest Homo, H. habilis, does not start until about 2 million years ago. Between those two time periods, “there is a big gap in the fossil record”, said anthropologist Brian Villmoare of the University of Nevada, Las Vegas, lead author of the new paper. Indeed, there wasn’t much more than “a handful of isolated teeth”, de Ruiter agreed.

With the hope of filling that gap, Villmoare and colleagues started scouring a site in the lower Awash Valley of Afar, Ethiopia, which geologist Ramón Arrowsmith of Arizona State University and his colleagues had confirmed contained sediments from 2.84-2.58 million years ago, as described in an accompanying Science paper. “One of the convenient things about East Africa,” said Villmoare, “is that it is a very volcanic area.” When a volcano erupted, he explained, it sent out ash containing crystals that started to decay and could be dated radiometrically. “When the ash lands it starts a timer ticking… so if you are between two ash layers, you know that you are sandwiched between those two dates.”

The specimen, which is from an adult and “likely female”, said coauthor William “Bill” Kimbel of Arizona State, exhibited a similar overall size to the jaws and teeth of A. afarensis, but had “somewhat slim” molars and a “more modern and less ape-like” canine area.

Ruth Williams/The Scientist