Thanks LibWhacker.
· join · view topics · view or post blog · bookmark ·
· post new topic · subscribe ·Google news searches: exoplanet · exosolar · extrasolar ·
Posted on 06/05/2022 7:14:57 PM PDT by LibWhacker
Eliminate the impossible, as Sherlock Holmes once said, and the truth, no matter how improbable, lies in whatever remains. Good advice for detectives — and, it turns out, for astronomers. Astronomy is often little more than piecing together scattered clues, carefully eliminating possibilities and arriving at an improbable truth.
Take, for example, the announcement of an exomoon discovery back in 2017. Observations seemed to show the presence of large moon, one as big as Neptune, orbiting a gas giant in a distant solar system. But, as the authors of the announcement were careful to state, the discovery was far from certain.
Follow up studies soon cast doubt on the claims. A team in Germany, reanalysing the data, concluded the signal could be coming from a hidden planet instead. But they were uncertain in their conclusion, arguing less that it was a planet and more that the possibility could not be ignored. The first study, they implied, was hasty in jumping to the idea of an alien moon.
Another team, this time at Harvard, saw no signs of anything unusual — moon or planet — at all. The signal, they wrote, was likely a data processing error. Since none of these possibilities can be eliminated, the existence of the exomoon remains in doubt; one improbable explanation amongst many others.
Not to say it is too improbable. Exomoons certainly do exist. Our Solar System is littered with moons — more than two hundred at the last count — and there is no reason why other solar systems would differ. But since moons tend to be small — none in the Solar System are bigger than Mars — finding one sitting light years from Earth is challenging.
Indeed, although astronomers have found thousands of planets scattered among the stars, they have yet to confirm the existence of a single moon beyond the solar system. That’s a shame. Since moons are so common, they offer a great deal of variety: from tiny rocks to ocean worlds bigger than Mercury. They host complex geology, hold vast oceans and have thick, chemically active atmospheres.
All that variety is reshaping the search for habitable worlds. Alien hunters at first focused their attentions on small rocky planets like Mars, attracted by their superficial resemblance to Earth. Yet decades of work has found nothing, and after ruefully admitting that few other likely planets are around, those hunters are now moving on.
The moons around Jupiter and Saturn look especially interesting. Deep underground oceans on Enceladus or Europa could, some argue, host simple life-forms. Traces of active geology, such as deep ocean vents, may offer an ideal place for chemistry to turn into biology. The result has been a burst of exploration: a crowd of probes are now preparing to visit Jupiter and its moons early in the next decade.
Those probes are likely to make some interesting discoveries; perhaps even hints of basic biology. Yet it is the other solar systems scattered across the galaxy that hold more potential. Telescopes have already picked out many bizarre planets, from boiling gas giants to frozen ice worlds and planets where rubies and diamonds fall as rain.
Astronomers have found many that could host life — some, indeed, that have been proclaimed as “more habitable than Earth”. That analysis is done based on their sizes and temperatures, factors that are fairly easy to judge across the span of light years. But moons, even if we can see them, will be harder to evaluate.
Some moons in our solar system appear warmer than a naive assessment would suggest. Enceladus, a moon of Saturn, should — based on its distance from the Sun alone — be frozen solid. Yet as it orbits Saturn the giant planet twists and flexes Enceladus’ core, releasing energy and heating the planet from the inside out. Enceladus thus hosts a vast liquid ocean under its frozen surface, one invisible at first glance.
Similar effects can be seen on many moons around Jupiter and Saturn — notably on Io, the most volcanic world in the Solar System. But life near a gas giant also has its downsides. Both Jupiter and Saturn are intensely radioactive: generating so much radiation that visiting spacecraft must take special precautions.
That, in short, means there is no simple test to say if a moon is potentially habitable or not. Certainly there is more potential: dozens of inhabited moons could be hiding in our data, circling planets we’ve dismissed as too cold or hostile for life. But detecting which are alive, and which are dead, promises to be more of a challenge.
Here there are no easy answers. Computer models can surely help, analysing which moons may be warm and calm enough for life to form. More advanced telescopes, too, are needed. In principle a powerful enough telescope could pick out trace gases in alien worlds; gases that might reveal biological or technological activity.
That might seem to discourage efforts, at least until our telescopes improve. But planetary scientists do have one more reason to hunt for exomoons. The discovery of thousands of exoplanets has revolutionised our understanding of how solar systems form and evolve. Exomoons could do something similar for planetary systems, revealing a myriad of ways in which planets and moons are born and live.
To fully understand the implications of all this — both for how planets form and for how widespread life could be — we need to start looking for exomoons. That, of course, is hard. Moons are small and faint. We are still discovering new ones even around Jupiter: nine were found in 2017 alone. Peering across light years to find them is, understandably, a great challenge.
Despite the difficulties, astronomers are beginning to try. Yet current telescopes — the obvious starting point — lack the power to pick out moons directly. Instead astronomers must do as Holmes advised, and hunt for intriguing clues that defy any other explanation.
A recent paper, published in Nature Astronomy, did just this. The team of researchers examined data from seventy exoplanets for traces of moons. To make the job easier, they focused on planets that look something like Jupiter: gas giants orbiting reasonably far from their parent stars.
That, they reckon, maximises the chances of finding moons. Models of planetary systems suggest that planets close to stars, like Venus or Mercury, rarely end up with satellites. Those farther out, like Jupiter or Saturn, seem to have dozens.
Of the seventy known gas giants that fit this description, only eleven showed signs of hosting a moon. Further investigation narrowed that to just three that looked like good candidates.
Taking a cautious approach — and following the advice of Holmes — they then sought reasons to eliminate each of those three. One, they concluded, was probably a false positive; an observational error caused by a shift in the position of Kepler, the space telescope that imaged it.
A second was also suspect. The team found the planet was orbiting a star marked by frequent large spots. One of those spots, they reasoned, might appear rather like a moon if seen in the right place. With that doubt in mind, the candidate was put aside.
The third looked much stronger. The team ruled out both instrument noise and star spots, and then looked for other explanations. Nothing came up — leaving the presence of an exomoon as the only remaining possibility.
From the data, it appears to be a large moon; one forty times bigger than the Earth. That — like the possible discovery of a Neptune sized moon in 2017 — is somewhat surprising. Theory suggests moons should generally be small, as are the ones found in the solar system.
On the other hand, given our limited observing abilities, perhaps we should not be too surprised. Any normal moon would be far too small and faint to detect at all. Only the truly bizarre examples should be visible — those, for example, dozens of times bigger than the Earth.
The first exoplanet discoveries followed a similar pattern. Those that were easiest to see, and thus the first to be seen, were giant planets orbiting close to their stars. Astronomers were initially puzzled: models based on our solar system had never predicted such possibilities, yet the galaxy seemed full of them.
As time went by, however, our measuring abilities improved. Astronomers started finding more normal looking planets, and a sense of stability returned to planetary science. The so called Hot Jupiters, although they initially looked common, turned out to be rare. The same relationship will likely hold for exomoons: at first we will discover strange and massive moons, before we start finding more familiar looking ones.
Things are likely to change fast. Just two candidate exomoons, both massive and only partially confirmed, are known. New telescopes, including the recently launched James Webb Space Telescope, will have the power to pick out nearby moons. Their numbers may well be about to explode.
Should the headline read: TWO New Telescopes?
Okay, I see it should read: TOO [the a colon]: New Telescopes ...
They may discover something else....
That’s no moon. It’s a space station
https://youtu.be/5WFCjnPNixM?t=70
That’s what I was thinking.
Doesn’t anyone understand the English language any more?
“I’ll have two hot dogs, please’’.
“There’s too many of you’’.
“I’m going to the store’’.
Almost all of our planets have moons. What’s the big deal?
Thanks LibWhacker.
· join · view topics · view or post blog · bookmark ·
· post new topic · subscribe ·Google news searches: exoplanet · exosolar · extrasolar ·
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.
