Though the object would have finally reached the very outermost edge of the Solar System many years ago, it would have taken a long time to travel to the balmy, central region where it was first discovered — and been gradually worn down into a pancake as it approached. This explains its unusual shape and its acceleration in one go, because the evaporating nitrogen would have left an invisible tail that propelled it forwards.
Pluto's Sputnik Planitia glacier is primarily made from nitrogen ice, and contains thousands of pits suspected to be caused by floating islands of water ice Credit: Alamy. For one thing, Loeb is sceptical that the Pluto-like planet 'Oumuamua came from would have had a large enough surface area for it to be statistically plausible that we have found a fragment of it. His team have calculated that you would need for the stars in the galaxy to have have times the mass they do, to account for us seeing a nitrogen iceberg that's been chipped off.
But if the theory turns out to be correct, 'Oumuamua may have provided a rare glimpse of what lies in alien solar systems. At the moment, we can only see the planets that orbit other stars indirectly — by how much light they block out as their silhouette passes in front of tthe stars, or though the way their gravity distorts light as they pass by. It's all down to the mind-boggling distances involved. Travelling the 4. If it left the Earth now, a spacecraft like the Voyager — which is currently exploring deep space just outside our solar system — would arrive in the year The fact that 'Oumuamua was still relatively large when it entered our solar system suggests that was still a pristine fragment of its parent planet, preserved in the icy vacuum of space for half a billion years.
In all that time, it is likely to have never encountered another star up close, until it stumbled upon our own. In particular, 'Oumuamua's possible identity as an icy nitrogen iceberg suggests that other solar systems are reassuringly similar to our own. Calculations have even suggested that the ice had a reddish tint, similar to the one found layered over Pluto's nitrogen glaciers, which contain methane. Before 'Oumuamua, the outer reaches of other planetary systems were a total mystery, because the objects there are too distant to form much of a silhouette against their neighbourhood star.
Even the nitrogen itself is news — in the Solar System, it's ubiquitous. But until 'Oumuamua, it was impossible to say whether it was common elsewhere. It's been recognised as the first interstellar comet ever found. It had a visible tail and was more or less what scientists were expecting. Based on its speed and trajectory, one international team has tentatively calculated that it might have originated around the star Ross — now a white dwarf — which inhabits a region of space around trillion miles trillion km away from the Sun.
They suggest that it was ejected into space after the violent collision of three large objects in this celestial neighbourhood around , years ago. However, Jackson is dubious. It was logical to assume that the same process would happen elsewhere in the galaxy — but totally hypothetical. Even after the discovery of 'Oumuamua, exactly how rare or statistically improbable its arrival was remained as baffling as the object itself — for all anyone knew its arrival might have been a once-in-a-lifetime event.
Equally, our solar system could be swarming with these fragments of the wider galaxy, which are so dark, they only show up when their path happens to take them right past the Sun. Now that scientists have found two interstellar voyagers, their hunch has been more or less confirmed. But estimating exactly how common these objects are — and how often we can expect to see them — remains extremely tricky.
One early calculation performed by Loeb and colleagues long before any interstellar objects were actually seen, in , looked at how likely we were to find a single one. They based their estimate on the density of stars in the Milky Way and assumptions about the amount of matter each of them is ejecting into the wider universe, then compared this to the sensitivity of the most powerful telescope on Earth.
By then, samples from Mars will have arrived back on Earth, perhaps containing concrete proof the Red Planet once harbored organisms or still does today.
And advanced telescopes on the ground and in space should be probing the atmospheres of potentially habitable exoplanets around nearby stars, looking for any that share the same biology-infused cocktail of gases as our own living Earth. As confident as astrobiologists may be that their quest will soon bear fruit, however, they are far less certain of how to communicate that success if and when it occurs.
They have been fooled before, after all. Last month in the journal Nature , a group of scientists came to grips with the problem. Their idea is to use a scale, from level 1 to level 7, that will allow confidence in any given case to be gradually increased. There is no shortage of cautionary tales from previous efforts to publicize apparent breakthroughs. The finding was not confirmed: later analysis poured cold water on the tentative evidence of Martian life.
Yet a repeat of that incident could now have disastrous consequences. More recently, the supposed detection on Venus of atmospheric phosphine, a possible biosignature gas, had many suggesting a biological origin, but that detection has itself since been called into question.
Deciding how to approach actual detections of biosignatures is a topic other scientists have been considering, too. Hundreds of scientists took part, with many in favor of more rigorous communications protocols.
If scientists were to adopt the CoLD scale, the first of its be seven steps, or levels, would be the actual detection of a potential biosignature. The online photos they study — taken by a medley of rovers and orbiters — make up a rich corpus of imagery for these highly motivated sleuths. But few of them are looking for fungi or other back-burner biology. They hope to find evidence of clever beings that either visited Mars or were once Red Planet natives.
It's a lovely and intriguing idea. It's also unlikely to pan out. Indeed, these homebody detectives just suffered another setback. In a paper published recently in the "Journal of Geophysical Research: Planets," scientists at Johns Hopkins University offer a simple explanation for the odd topography of an artifact that some mistook for a crashed alien spaceship.
They say the purported spacecraft is actually something only a geologist could love — the handiwork of ancient volcanism, not Vulcans. The artifact is located in a region of Mars known as the Medusae Fossae Formation. It's a strange-looking geologic deposit the size of Alaska and Texas combined. NASA is planning a mission to Jupiter's moon Europa to search for signs of alien life on the icy, ocean-harbouring world.
Life could exist on exoplanets planets attached to stars other than our Sun. The Kepler spacecraft identified unconfirmed planetary candidates. Have you read these stories? RBI's retail direct gilt scheme: How to invest? ET NOW. Brand Solutions. Video series featuring innovators. ET Financial Inclusion Summit.
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