The Week in Space and Physics

On the future of space stations, exoplanet atmospheres, panspermia and black hole craters.

The International Space Station is the largest - and most expensive - thing we’ve ever constructed in space. Sometime in the next decade or two, however, the station will be abandoned, its systems switched off, and then, carefully, it will be pulled back down to Earth.

That raises some interesting questions about the future of human spaceflight. For the past few decades the space station has been the focus of almost every manned trip into orbit. When the station is retired, what where will that focus shift?

One obvious answer is the Moon. NASA and China have ambitious plans to visit and explore the lunar surface. Both are seeking partners from around the world, building two rival international coalitions in pursuit of the Moon. NASA hopes to send astronauts by 2024 - though 2028 may be more realistic. China, if all goes to plan, will follow a few years later.

To that end America is already planning to build a new space station, the Gateway, in orbit around the Moon. The envisioned structure is, however, far smaller than the International Space Station and probably would not be permanently inhabited. Instead it would serve as a base for astronauts visiting the Moon; a temporary home far from Earth.

Relying on the Lunar Gateway alone, then, would represent a loss of capabilities for the American space agency. Without a station in low earth orbit, NASA would be severely restricted in the amount of research it can perform. Since China is constructing a station of their own, that may give the impression America is falling behind.

Fortunately, NASA is looking at other options. Instead of a state funded facility, however, America is hoping that commercial parties will step in. NASA seems to imagine a future where several commercial space stations fill Low Earth Orbit, while the agency focuses its attention on the Moon, and - perhaps - Mars.

Tentative first steps towards this have been made with the Commercial Low Earth Orbit Development (CLD) program. Around a dozen companies have sent NASA proposals for stations they could build in orbit. Perhaps three or four of those proposals will be chosen for further funding - with several hundreds of millions of dollars available for the winners.

Those stations will not, however, come anywhere close to the capabilities of the International Space Station - which cost at least $150 billion. That means, unless NASA is willing to somehow extend the life of the existing station, America will almost certainly have to accept a reduction in its in-orbit capabilities.

Some politicians are already warning about the geopolitical risks this raises. They are concerned about the prospect of a space station gap - a possible period at the end of this decade when America is left without any functioning station in orbit. Avoiding that is crucial, they argue, to prevent falling behind China in an important strategic arena.

One option for NASA is to expand existing commercial agreements. Axiom Space, a private venture, will soon add their own modules to the space station. With more money, and encouragement, they could transition to building their own station. NASA will need more funding too - even if only to extend the life of the International Space Station.


Cloud Watching on Alien Worlds

Roughly five hundred light years away lies one of the strangest worlds we have ever discovered. Though WASP-127b is a gas giant - something like Jupiter or Saturn - it looks almost nothing like them. Indeed, by mass the planet is much smaller than Jupiter, just a fifth of its size. By diameter, however, the planet appears almost a third bigger.

That strange combination, which makes the planet one of the least dense known, might be caused by its odd orbit. WASP-127b lies close to its host star, completing a single revolution - a year - in just four days. That means surface temperatures are searing - likely more than a thousand degrees Celsius.

Such extreme conditions have probably puffed up the gas layers of WASP-127b, creating a wispy but far reaching atmosphere. Such an atmosphere is unusual - but also much easier to spot through our telescopes. To that end, astronomers have dedicated time on several occasions over the past few years to scoping out the planet.

Back in 2018 such a study revealed the presence of alkali metals - sodium, potassium and lithium - in its atmosphere. They also found, though the evidence was not solid, traces of water. This, the researchers suggested, shows the plant had relatively clear, cloud free skies - one of the first times we have been able to say much about the weather on a distant planet.

Now a new report has analysed the atmosphere in greater detail. Using both the Hubble Space Telescope and the Very Large Telescope in Chile, a team of astronomers were able to study different regions of the atmosphere. Again, they detected signs of metals like sodium, but much lower in the atmosphere than previously thought.

Traces of water vapour were also visible, as before. This time, however, the data suggests that plenty of clouds are actually present in the atmosphere, and that they are blocking much of the light we should see from water layers deeper down. Unlike clouds on Earth, however, these clouds are not made from water vapour. They seem to be composed of droplets of some other substance - though quite what remains mysterious.

Studies have also found that the planet is in a retrograde orbit - meaning it rotates around the star in the opposite direction to the star’s own spin. Such an arrangement is unusual, and should be unstable. Given the age of the planet - around ten billion years - this suggests something has disturbed the solar system recently.

It is possible, astronomers think, that WASP-127b was originally much further from its star. The planet may then have appeared more normally, perhaps something like Neptune in our own solar system. But after a disturbance - exactly what is unclear - the planet was pushed inwards.

Then, exposed to the sweltering heat and radiation of its star, the planet started to morph into the strange world we see today. Its atmosphere would have puffed up - and perhaps started to erode, stripped away by the force of the star. Our observations of WASP-127b might, then, betray a tragic past.


Life in Space

Lichen, it seems, are hard to kill. Back in 2005 a team of researchers deliberately exposed a capsule of them to the full harshness of space. They remained there for two weeks, experiencing a near total vacuum, freezing temperatures and regular doses of ultraviolet radiation.

That should kill almost any living thing, but the lichen, the researchers found, still appeared perfectly healthy. Once back on ground they fully recovered within twenty-four hours, growing much as they had before their exposure to space.

That lent support to the theory of panspermia, the idea that life can hitch cosmic rides from planet to planet, and perhaps even from star to star. If lichen can survive in space, perhaps on a rock blasted upwards after an asteroid impact, then it seems possible that they may one day find themselves falling on an alien world.

Nowadays most planets in our Solar System are too inhospitable even for lichen to thrive. But billions of years ago, when the Sun shone less brightly and Mars still held its atmosphere, the story could have been different. Life may even have started elsewhere in the Solar System - perhaps on Mars or Venus - and then migrated to Earth on space rocks.

The idea that life could have travelled between the planets is not, then, quite so far fetched. But what about between stars? We know that comets and meteorites occasionally traverse the vast interstellar distances. Could life somehow hitch a ride?

In order to do so, any life - lichen or otherwise - would have to survive millions of years exposed to the harsh environment of space. Whether anything, even in a dormant state, could do that is completely unknown. Assuming, however, that it is possible, a team of researchers based in Chile, France and Korea have worked out a model of how life could spread through a galaxy.

Using a sophisticated model of galactic dynamics, they calculated the potential habitability of thousands of stars scattered across a galaxy. That, they found, increased the further a star is from the galactic centre - a factor that influences how often supernova blast a world with deadly radiation.

The probability of panspermia, they concluded, behaves differently. Stars near the galactic core are closer together, making it easier for rocks and comets to move from star to star. But the more habitable stars, further away, are spread more thinly. That makes it harder for life to spread from one to another.

The overall result suggests that life could indeed spread across a galaxy. But the model finds the effect to be slight - life would spread to less than three percent of all stars. That, the researchers think, makes the old fashioned way of starting life - in some warm little pond, perhaps - the dominant force in the universe.


Lunar Traces of Black Holes?

At the centre of our and almost every other galaxy lies a supermassive black hole. Some astronomers also believe the universe should be teeming with tiny black holes formed in vast numbers during the Big Bang. They could, indeed, be so widespread that they account for the invisible extra mass known as dark matter.

Even though some theories predict the presence of these black holes, no experimental proof of their existence has ever been found. Black holes are, naturally hard to spot - they emit no light, and even supermassive ones can only be seen by their effects on surrounding matter.

Despite this, some astronomers have suggested ways we might spot smaller ones. Some speculate that the Tunguska blast - a mysterious explosion in Siberia a century ago - could have been caused by a small black hole. Others wonder if a planet sized black hole lurks at the edge of our solar system, creating patterns of gravitational disturbances.

Now, according to an article in New Scientist, some researchers have proposed searching the Moon for traces of ancient black hole impacts. Such a collision would leave a unique fingerprint - as the black hole passed through the Moon it would leave a long tunnel of molten rock. On the surface that would look like a steep crater, far steeper than those left by meteorites.

Even so, as the article points out, finding such a crater will be challenging. Some astronomers think any traces of a black hole collision would soon be erased, the craters obliterated by other asteroids. Others argue that the number of black holes that would have hit the Moon, even over billions of years, is tiny.

That means, then, that searching for traces of black holes on the Moon is unlikely to bring much luck. Astronomers will need to find another way to find the tiny black holes that could litter the cosmos. Fortunately they seem to have no lack of creative thinking.


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