The Week in Space and Physics
Rogue planets, solar sails and tiny satellites, life on Venus and the threats of mega-constellations.
The vision is chilling: a world with no sun, cast adrift in the vastness of space, blanketed in an eternal darkness and doomed to lose every last watt of heat it possesses. The freeze, once it comes, will be unending; an icy grip that strangles the planet and extinguishes hope forever.
This horrifying fate may have befallen thousands, if not millions, of worlds in our galaxy. Astronomers name the victims “rogue planets”: abandoned worlds floating forever across an uncaring cosmos. A handful have already been found, mostly by sheer chance as they happen to drift past our solar system.
They are hard to detect. Most techniques for finding exoplanets rely on the presence of an easily visible star. Planets create regular disturbances as they orbit their parent star, disturbances that astronomers have learned to spot. For planets adrift in the void, however, these techniques are useless.
The few that we have seen were hot planets, newly formed worlds that have yet to lose the heat of creation. Telescopes can pick up their glow, which reveals them to curious astronomers. But this accounts for a tiny fraction of the planets that should surely be out there.
Those, though, are frozen worlds. They emit no heat or light, rendering them all but invisible. Instead, as a team at Manchester University announced last week, astronomers must turn to another property to spot them: their gravitational fields.
Though small, these fields are strong enough to create an odd effect predicted by Einstein’s theory of relativity. Whenever such a planet passes in front of a far away star, its gravitational field acts to slightly bend and focus that star’s light. The result is a momentary brightening, one that telescopes can pick out. Astronomers look for stars that match this pattern and then work backwards to identify the rogue planet.
The team at Manchester University looked at the night sky near the heart of our galaxy, a place dense with stars. They found five clear examples of this effect, which, the researchers think, shows the presence of four rogue planets and one previously undetected star.
The data the team used was originally intended for other purposes. Fortunately the astronomers were able to repurpose it, but with a dedicated telescope they could certainly find many more examples. The world of exoplanets may be about to get a lot darker, and a lot more chilling.
Ever smaller satellites are changing the face of space technology close to Earth. Smaller, cheaper satellites allow companies to build out vast constellations - as SpaceX are doing for communications and others have done for earth observation. But what about space exploration far from Earth?
Traditionally this has involved expensive, long-term missions to distant parts of the Solar System. Building a probe to reach Saturn, for example, can take a decade or more, before another decade is spent in flight to the ringed planet. Miniaturisation, however, may soon change that picture.
Small satellites are not, on the face of it, well suited for long journeys into the heavens. They carry limited resources, from electrical power to propulsion, and lack the powerful antennas needed to communicate over vast distances.
But their small size also confers big advantages. They are cheap and fast to build - allowing rapid iteration and turnaround of ideas. They can operate together in fleets, opening up new possibilities for missions. And they allow a level of standardisation and mass production that has so far been missing in space exploration.
These advantages are tempting enough for space agencies to look for solutions to their drawbacks. NASA has so far funded several small satellite missions for deep space purposes, including the MARCO mission to Mars in 2018. Now they are planning a more ambitious test: sending a small probe to an asteroid.
The mission, NEA Scout, will be launched later this year as part of the Artemis I flight to the Moon. To make up for the limited propulsion onboard, the spacecraft will deploy a solar sail: using sunlight alone to steer it to its destination. Once there, the probe will take a series of photographs, casting light on the structure of these potentially hazardous objects.
More importantly, it will test the solar sail - a technology long mooted as a game-changer for long space voyages, but one so far little tested in reality. The probe will be a key test for small satellites far from home, and, if successful, may be an opening shot of a new era of exploration.
Last year, researchers announced startling signs of biological activity on Venus. Scientists found traces of the gas phosphine in the planet’s atmosphere, suggesting that some unknown process - perhaps biological - had put it there.
The discovery made headlines around the world, but soon turned out to be much more controversial than it had first appeared. As astronomers scrambled to confirm the presence of the gas, they realised the telescope making the observation had erred, processing the data it generated incorrectly. The revised numbers drastically reduced the amount of phosphine present in the atmosphere.
Other astronomers, re-analysing older observations of Venus, found strange signs of other gases that shouldn’t be there. Once again, this strengthened the argument that something odd was happening on the planet. Then, in June this year, another team of researchers found the atmosphere of Venus was far too dry for even the hardiest of life forms to exist, dampening expectations.
Now scientists have proposed an explanation for all this that doesn’t invoke biology. Researchers at Cornell University argue that volcanoes on Venus are enough to explain the phosphine seen, if the planet is somewhat more volcanically active than previously thought.
That could chime well with other research indicating the presence of active geological processes on Venus. Scars and fractures on the planet’s surface seem to indicate that parts of the crust still move, creating earthquakes and volcanoes.
All this interest in Venus is welcome, as the planet has long been ignored in favour of Mars. Though the initial signs of biology have turned out to be wrong, the buzz it created has led to at least three new missions to explore and investigate the planet over the next few years. We may be about to discover a lot more of Venus’ secrets.
The growing number of satellites in orbit is starting to cause concern among scientists. Two chief worries stand out: that the risk of collisions is rising, and that the vast numbers of objects in the skies threaten Earth-based astronomy.
The first worry has been around for a while, long enough to have a name: Kessler Syndrome. This is the idea that each collision in space raises the risk of future collisions, eventually resulting in a cascade of destruction. The prospect is concerning, though in truth we are still some way off it becoming a serious issue.
The majority of the new satellites are low enough to still feel the effects of the Earth’s atmosphere. That means that if they fail, or collide, they will naturally be pulled back down to Earth within a few years. That offers a safety check, of a kind. Even if the worst does happen, and a Kessler Syndrome wipes out low Earth orbits, the debris would clear within a few years.
Perhaps more of a concern for the future is the growing threat to astronomy. Elon Musk’s satellites have captured the world’s attention, forming easily visible “trains” of light passing across the night sky. While many find this a stunning symbol of our technological age, astronomers have watched with horror.
The bright lights from these satellites smear streaks across otherwise perfect astronomical images. Astronomers can cope, just about, but they worry that plans for more satellites will make it ever harder to photograph distant objects.
So far the question of who gets priority - satellites or astronomers - is unsettled. But astronomers are now reaching out to the United Nations to push their case. They argue that humanity has a right to dark and quiet skies, a right that is being infringed by the likes of Starlink. The fight, in all likelihood, is just beginning, but at its heart lies a deep question: Who owns the night sky?
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