Since the momentous discovery In 1992 Two planets orbiting a star outside our solar system, thousands of new worlds added to the rapidly growing list of “exoplanets”. In the Milky Way galaxy.
We learned a lot from it an extensive catalog of alien worlds orbiting alien stars. But one small detail sticks out like a sore thumb. We have found nothing there but our own solar system.
This has led some to conclude that our host star and its progeny may be somehow out there – perhaps the only planetary system of its kind.
Additionally, it can mean that life itself is alien; The conditions that formed the Earth and its self-replicating chemical mantle are difficult to replicate.
If you just look at the numbers, the outlook is grim. By a large margin, the largest number of exoplanets we have identified to date are of a type not known to be suitable for life: giants and subgiants, the gas and possibly ice variety.
Most of the exoplanets we’ve seen so far orbit their stars very closely, practically hugging them; so close that their sizzling temperatures would be well above their known habitable range.
It’s possible that as we continue to search, the statistics will balance out and we’ll see more places that remind us of our own backyard. But the issue is more complicated than looking at the numbers. Exoplanet science is limited by the capabilities of our technology. Furthermore, our impression of the true diversity of alien worlds risks being limited by our own imaginations.
What happens in the Milky Way galaxy and beyond may be very different from what we actually see.
Expectations and how to avoid them
Exoplanet science has a history of defying expectations from the very beginning.
“If you go back to the world I grew up in, we only knew one planetary system” University of Southern Queensland planetary scientist Jonti Horner told ScienceAlert.
“So it was this sort of tacit assumption and sometimes overt assumption that all planetary systems would be like that. You know, near the star you’d have rocky planets that are pretty small, and far away from the star you’d have gas giants that are pretty big. Planetary systems would be the same.”
This is why it took scientists a while to identify an exoplanet orbiting a main sequence star like our Sun. Assuming other solar systems are like ours, it would take years to observe the telltale signs of heavy planets orbiting their stars, just as our own gas giants take years to complete their orbits.
Based on such long durations of a single measurement, it would not be worth sifting through a relatively short observational history to definitively filter out many stars in the other main sequence solar system.
Finally, when looking The exoplanet they found was unlike anything else what did they expect: gas giant half the mass (and twice the size). Jupiter Orbiting very close to its host star, its year is 4.2 days long, and its atmosphere burns at about 1,000 degrees Celsius (1,800 degrees Fahrenheit).
Since then, we’ve learned that these “Hot Jupiter”-type planets aren’t so strange after all. If anything, they seem relatively generic.
We now know that there is much more diversity in the galaxy than we see in our home system. However, it’s important not to assume that what we can currently detect is all the Milky Way has to offer. If there is anything like our solar system out there, it may be beyond our detection capabilities.
“Things like the solar system are very difficult for us to find, they’re technologically a bit beyond us,” says Horner.
“Trestic planets would be very unlikely to be picked up in any of the surveys we’ve done so far. mercury, VenusEarth and Mars Around a star like the sun.”
How to find a planet
Let’s be clear: methods we use to discover that exoplanets are incredibly intelligent. There are currently two in the workings of the exoplanet detection toolkit: the transit method and the radial velocity method.
Either way, you need a telescope that is sensitive to very small changes in a star’s light. The signals each was looking for could not have been more different.
For the transit method, you need a telescope that can keep the star fixed in view for a long time. That’s why instruments like NASA’s space-based Transiting Exoplanet Survey Satellite (TESS) are such a powerhouse that can be locked into a segment of the sky. More than 27 days Uninterrupted by the Earth’s rotation.
An exoplanet gif invading astronomy! This time with a gif showing the transit method for detecting exoplanets 😊 pic.twitter.com/2ZHv24DRTH
— Alysa Obertas (parody) (@AstroAlysa) September 1, 2021
The goal of such telescopes is to detect a transit signal—when an exoplanet passes between us and its host star as a small cloud that blots out some of the sun’s rays. As you can imagine, these light drops are small. And one strike is not enough to confidently infer the existence of an exoplanet; there are many things that can extinguish a star’s light, many of which are one-time events. Multiple transits, especially those that exhibit regular periodicity, are the gold standard.
Therefore, larger exoplanets with short orbital periods, closer to their stars than Mercury is to the Sun (some very, very close, in orbits less than an Earth week) are favored.
In case you missed it, my gif showing how exoplanets are detected using the radial velocity method is now available in dark mode! pic.twitter.com/P4yvXQVSUt
— Alysa Obertas (parody) (@AstroAlysa) August 15, 2022
The radial velocity method detects the wobble of the star caused by the gravitational pull of the exoplanet as it rotates in its orbit. As you can see, the planetary system doesn’t revolve around the star so much as it dances in a coordinated mess. The stars and planets revolve around a mutual center of gravity known as the barycenter. For the solar systemit is primarily a point very, very close to or beyond the surface of the Sun. Jupiterwhich is more than twice the mass of all the remaining planets combined.
Unlike the blink-and-miss phenomenon of a transit, the change in the star’s position is a continuous change and does not require constant monitoring to notice. We can detect the rotational motion of distant stars around their barycenters because this motion changes its light Because of something called the Doppler effect.
As the star moves toward us, the light waves coming our way are compressed slightly toward the bluer end of the spectrum; the further away the waves stretch towards the redder end. A regular “wobble” in the star’s light indicates the presence of an orbital companion.
Still, the data favor larger planets with stronger gravitational pull on shorter, closer orbits to their stars.
Apart from these two prominent methods, it is sometimes possible to directly image an exoplanet orbiting its star. Although it is a very difficult task, it can become more common During JWST.
According to Daniel Bayliss, an astronomer at the University of Warwick in the UK, this approach will almost certainly reveal the opposite class. to the short orbit variety of the exoplanet. To see an exoplanet without being swamped by the glare of its parent star, the two objects need to be separated very widely. This means that the direct imaging approach favors planets on relatively long orbits.
However, for obvious reasons, larger exoplanets can still be detected more easily with this method.
“Each discovery method has its own biases,” Bayliss said.
Earth, which has a year-long orbit around the Sun, sits between the orbital extremes favored by various detection methods, so “finding planets with one-year orbits is still very, very difficult,” he adds.
What is there?
from far away is the largest group exoplanets are a class not even represented in the solar system. This is a mini-Neptune – gas-covered exoplanets smaller than Neptune and larger than Earth in size.
Most confirmed exoplanets are in shorter orbits than Earth; in fact, more than half have orbits of less than 20 days.
Most of the exoplanets we found orbit single stars similar to our Sun. Less than 10 percent are in multi-star systems. still mMost of the stars in the Milky Way are members of multi-star systems, and it is estimated that up to 80 percent share orbits around at least one other star.
Think about that for a moment. Does this mean that exoplanets are more common around single stars, or that exoplanets are harder to detect around multiple stars? The presence of multiple light sources could distort or obscure the very similar (but smaller) signals we try to detect from exoplanets, but it could also be argued that multi-star systems somehow make planet formation more difficult.
And that brings us back home to our Solar System. As odd as the house may seem in the context of everything else we’ve found, it may not be unusual at all.
“I think it’s fair enough to say that there are very common types of planets that don’t exist in our Solar System,” says Bayliss.
“Super Earths, which are a bit like Earth but with twice the radius, we don’t have that. We don’t have these mini-Neptunes. So I think it’s fair enough to say that there are very common ones. Planets that we don’t see in our solar system.
“Now, whether that makes our solar system rare or not, I think I wouldn’t go that far. Because there could be many other stars with solar system-type sets of planets that we can’t see yet. .”
On the verge of discovery
The first exoplanets were discovered orbiting only 30 years ago pulse, a star completely different from ours. Since then, the technology has improved by leaps and bounds. Now that scientists know what to look for, they can develop better and better ways to find them around more and more different stars.
As technology advances, so will our ability to find smaller and smaller worlds.
This means that exoplanet science may be on the verge of discovering thousands of worlds hidden from our current view. As Horner points out, there are more small things in astronomy than big things.
Red dwarf stars are a perfect example. They are the most common type of star in the Milky Way, and they are small, about half the mass of the Sun. They are so small and faint that we cannot see them with the naked eye, but they count Up to 75 percent of all the stars in the galaxy.
Right now, when it comes to statistically understanding exoplanets, we’re working with incomplete data because there are worlds we simply can’t see.
This is bound to change.
“I just have this nagging feeling that if you come back in 20 years, you’re going to be as skeptical as you are of those statements that mini-Neptunes are the most common type of planet. In the early 1990s, it said you would only get rocky planets near the star,” Horner tells ScienceAlert.
“Now, I could be proven wrong. That’s how science works. But I think that when we get to the point where we can discover things that are Earth-sized and smaller, we’re going to see that there’s more. Earth-sized and smaller than Neptune-sized.”
And maybe we’ll see that our strange little planetary system isn’t alone in space with all its oddities and wonders.
