The Exoplanets Next Door

[00:00:00]hi so 32 years ago and that's within my lifetime and probably many of yours scientists discovered for the first ever time planets outside of the solar system now if you've been around for a while you might remember the very first video I ever made on this channel was about these types of planets which are called exoplanets note that I will be using the word planets in this video but I mean it in a colloquial sense because technically Planet only refers to the eight planets of the solar system now these first two exoplanets were pretty weird being an orbit around a neutron star and all but then 29 years ago scientists discovered the first planets around other stars that were like the sun now this was a really big deal they actually kind of got a Nob prize for it which like sorry to the guys that found the Pulsar planets now this Planet 51 Pegasus B was also very weird because it's a gas giant planet like Jupiter but it was orbiting closer to its star than Mercury orbits to the sun weird we actually know of a lot of these now and they're called hot Jupiters so new exoplanet discoveries continue to come in over the years more and more indicating that exoplanets are actually pretty and then 8 years ago and this was certainly within your lifetime and if it wasn't dear Gods where are your parents we found a planet orbiting Elfa centuri C now if that name doesn't sound familiar to you you might know this star by its other name Proxima centuri Proxima as in close yes that's right the star that is the closest to the Sun in the entire universe has planets how [ __ ] cool is that exoplanets right next door just over four Lighty years away wa wait exoplanets as in plural yes so there have been three exoplanets found in the proximus centari system one of which has been confirmed and two of which are still candidates I just want to pause for a moment and appreciate how absolutely mindboggling this is 32 years ago we didn't know if planets and other solar systems existed at all and now we know that there are multiple planets in the nearest star system to the sun you can see why I chose to study exop planets for my PhD okay so let's talk about the star now I said it name was Alpha centuri C and that might hint to you that there is an alpha centuri A and B and you would be correct this is a triple star system Alpha centari A and B are the big boys in this system they're pretty similar to the Sun and they orbit pretty close to one another at a semi major axis of around 23 a alpha centuri C on the other hand is kind of just over here doing its own thing because it orbits the other two at a semi- major axis of around 8500 Au and this kind of separation between the close binary and the wide prary component is how this three body system can stay stable Proxima is also just a small star it's only about 12% the mass of the Sun making it a kind of star called an mdor its surface temperature is only around 3,000 Kelvin which is a little bit more than half the surface temperature of the Sun and while it is hot enough to melt things like niobium and malinam it's not hot enough to melt tungsten like you could put my husband's weather ring in the atmosphere of this star and it wouldn't melt so as far as the surface of a star goes that's pretty chilly bring a coat okay so that's the star proxus centari what about the planets let's go in reverse order so the way that exoplanets are designated is that they get a letter a lowercase letter based on the order of Discovery starting with the letter B since there are three of them that means we're going to be going d c b in this case Proxima centuri D is actually the innermost Planet orbiting at a distance of just 03 Au that's really close I mean Mercury orbits the Sun at just under4 Au now I said the letter D indicates that this was the most recent discovery and indeed proxen D was only proposed as a planet candidate back in 2022 Based on data that was taken in 2020 and one reason that it was so hard to find this planet even though it's really close to the star which generally makes it easier is because this planet is so freaking small it's about a quarter the mass of the Earth they use the radial velocity technique to discover this planet which basically looks at how much the star is moving because of the orbit of the planet as you can imagine a planet a quarter of the mass of the Earth does not make a star move very much even if that star is a pretty small star like proxen in fact the signal for this is about 40 cm per second now maybe that doesn't mean anything to you but I promise that this is a really really difficult measurement to make in order to find this signal they had to use a very very high resolution spectrometer called espresso that was mounted on the VT yes that's the very large telescope no I did not come up with this name this signal is so small that at the time Proxima centari D was the least massive planet ever discovered by the radial velocity technique and I think it still holds that title actually now even though Proxima centuri is pretty cold for a star this planet is orbiting so close that it's really hot its equilibrium temperature is possibly around 3 60 Kelvin which is 188° f for context the equilibrium temperature of the earth is about 0° fenit proxen is Toasty for sure so yeah it's pretty cool that we were even able to detect this hot little exoplanet neighbor so if you know your alab bit before D comes C and Proxima centuri C was proposed as a candidate back in 2020 a pandemic planet now this is actually the outermost of the three planets and it orbits at a distance of around 1 and A2 Au which is basically how far Mars orbits from the Sun now Proxima centari C was also detected by the radial velocity technique and since it's so much further out in the system you might expect that it's a much bigger planet and you would be correct the mass is estimated to be somewhere around seven times the mass of the earth now there are no planets like this in the solar system but this kind of mediumsized super Earth or mini Neptune planet is actually really common among exoplanets now the signal for proxin C was detected by a different higher resolution spectrograph called Harps which is kind of a previous generation so it's not quite as high resolution as espresso and harps is mounted not on the 8.2 M VT but on the 3.6 met telescope at the lasia observatory but these are both ESO telescopes that means both proxen D and prox andc are ESO discoveries now something in astronomy that I think is just so cool is called precovery so this basically means that once you detect something you go back and you find it in older data that's pre-existing data from before the discovery but you didn't know it was there until you knew to look for it if that makes sense so a couple astronomers did this for proxen C and went back and looked at Hubble data from the '90s and thought that they might have found an astrometry signal that was corresponding with proxin now because Proxima centari C is so far from Proxima centuri it's actually a pretty good candidate for what we call Direct Imaging that is being able to see the planet directly instead of only seeing its effect on its star so in 2020 a group of astronomers looked for this direct Visual Evidence of Proxima centari SE and they found something basically there was some signal there that could have lined up with Proxima centar C but it wasn't a clear detection and they couldn't really confirm it and then in 2022 after the discovery of proxen D some astronomers came up with a new algorithm for evaluating this radial velocity data and they went back to the harps data and they used it for Proxima centuri and they were able to see that signal from proxen D but they didn't see the signal for proxen C and the RV signal of proxen C should be larger than that of proxen D so they disputed the existence of proximus andar and said that the initial detection was probably just unaccounted for systematic effects and as far as I know that is still where things currently stand with proximus and TC it is a planet candidate that has been disputed but has not been confirmed or rejected so after d and c we come to B in the case of Proxima centari B we were saving the best for last see proxin B is the middle planet and while proxen D is real hot and proxen C is real cold proxen B is just right yes proximos centari B is located in What's called the habitable zone or sometimes called the goldilock Zone where basically conditions are just right for liquid surface to exist on the surface of a planet it's really important to note here that being in the habitable zone does not mean that a planet definitely has liquid water on the surface and even if it does it doesn't mean that it's necessarily habitable or that it has life on it it's basically just a minimum qualification for Life as we know it necessary but not sufficient for a teeny little star like proximus centuri that means that the H zone for an earthlike planet is just eyeballing it here about 04 to 09 Au that's really close and proxen B it orbits at 049 AU so it is right squarely in the middle of that habitable zone baby it's actually a little bit further out in its habitable zone than Earth is in the sun's habital zone so it's equilibrium temperature it's a little bit colder about - 38° F or 230 something K but if that estimate of the habitable zone is for earthlike planets how earthlike is proxen B I mean we have proxen D which is so tiny that even if it wasn't super hot and it was in the habitable zone it's so small it might not be able to hold on to any water I mean just look at Mars and then proxin B is actually big enough that it might not even be a rocky planet it might be more like Neptune with this really really thick atmosphere without a radius measurement we can't really know for sure but proximus centari be it is within just a few perent of the mass of the earth now we don't know its radius but at that mass it is most likely to be a rocky planet so oh my gosh one of the three nearest exoplanets to us in all of the Galaxy is an earthlike planet in the hatle zone of its star I know I already used the word mindboggling but I really can't think of another word it's just it's mindboggling it's so amazing but before you get carried away thinking about little green men running all around this planet that's just a little over four light years away there are a few more factors that are important to consider so I said that the habitable zone around an mdo star like Proxima centuri is really close to the star and that means that the planets that are orbiting in that zone are likely to be tily locked to the star this is like how the Moon is with the Earth where the same face of the moon is always facing the Earth but in this case it would be the same face of the planet always facing the star now it's not impossible that tidy locked planets are habitable but it's a pretty big difference from how the Earth operates the one side that's facing the star is going to be getting just so much more energ it's going to be way hotter than the other side have you ever Sat by a fire on a cold night and your face feels like it might just melt off but your back is freezing it's like that for some tiny locked planets that might mean that the star side is just way too hot and the other side is just way too cold but there might be life around the Terminator or that kind of in between permanent Twilight area now for proxen B because it's further out in the system it's a little bit colder so instead of being this like unbearably cold unbearably hot Dynamic it might be an ice ball but the side that's facing the star has melted a little bit so that actually might be where the liquid water is on the planet we don't know for sure there are a lot of factors that go into modeling the climate of a planet and we just don't have enough information about proximity to do this with accuracy but there are some proposed models that would have a habitable area on the planet now another thing that's really nice for habitability is an atmosphere and not just for breathing although you know we do like to do that see the boiling point of water is very dependent on pressure and the pressure on a surface of a planet usually comes from the atmosphere so without enough atmosphere to provide pressure the water on the surface of a planet can just boil away well technically it would be sublimating away but that doesn't really have the same ring to it another nice thing about the atmosphere is this little feature you may have heard of called the ozone layer here on Earth the ozone layer actually protects us from some of the harmful radiation coming from the Sun in the form of UV rays UV light is not kind to cells but on the other hand the atmosphere can be kind of not cool for life I mean think of Venus it's got a nice thick atmosphere a little too thick if you know what I mean and do we know anything about the atmosphere on proxen B no we do not so this is a big unknown and that's just the planet there's also these Stars I've talked a lot about how proximus centuri is really small and it has this really low flux but that's not the only way the M dwarf stars are different M dwarf stars tend to be really really flarey Stellar flares are these really big bursts of concentrated radiation and M dwarf stars just flare a lot more than gwf stars like the sun and the radiation in flares is really high energy like those UV rays that are so harmful to humans and even extreme ultraviolet rays called XUV and since the habitable zone is so close to the star there's a lot less distance for that radiation to dissipate over because radiation kind of dissipates on this inverse Square law so a little change of difference makes a really big difference in how much radiation you're getting so these planets that are in the habitable zone of M stars are just getting blasted by radiation like a lot and it's not just the radiation because these Stellar winds which is like charged particles and stuff is also really really strong so all this UV radiation and the cellar winds this can cause a planet to lose its atmosphere and even its water and if that radiation is getting down to the surface it could basically just be like sanitizing the surface of any light and how much of that reaches the surface Can Depend a lot on whether or not proxy and B has a magnetosphere and we again don't know this but then again maybe it's not all bad and if the planet does have an atmosphere and a magnetosphere all that XUV flux can actually help create ozone which could create an ozone layer in that atmosphere which could help protect its surface basically as you can probably tell from how much I've been talking about it over the past 5 to 10 minutes habitability is really really complicated and for nwarf stars is even more complicated because they're just so different from solarik systems and we have no idea about life in nonso like systems we have a one single sample and it's around a g dwarf not an M dwarf so is Proxima centari B habitable does it have liquid water does it have an atmosphere we do not know any of this as you can imagine Proxima centu B is of really high interest to scientists so it's going to be continued to be observed by ever more powerful telescopes it's even being monitored for techno signatures because we really want to learn as much as we can about this Earth next door and answer some of these open questions we have about it now one last but definitely not least thing to consider is that while Proxima centari is really really close to us astronomically speaking four and some light years is really really far in Practical terms consider the Voyager missions which are basically some of the fastest spacecraft that humans have ever launched they're bwing about 177,000 m/ second which is like 0.006% the speed of light I think it's slow cosmically speaking they've actually both entered the interstellar medium and are over 100 Au away from the Sun but even so well for one thing neither of them are headed towards Alpa centari but even if they were it would take them over like 73,000 years to get there and that's assuming that Proxima centari wasn't moving in the meantime in actuality proximus andari and the sun are moving relative to one another so it wouldn't even it just wouldn't happen but just to illustrate the current distant with some context it's very far over the decad there have been several Mission ideas proposed to visit Alpha centuri even before we knew about these exoplanets around Proxima centuri but they're all basically science fiction they're just not feasible with our current level of Technology probably the most realistic proposal is called breakthrough star shot which seeks to use a swarm of really really low mass probes that are propelled by light sails to fly by Proxima centuri if you have powerful lasers like really powerful gigawatt lasers shining directly onto these light sails you could potentially accelerate them up to about 20% the speed of light which would make the trip only last you know a few decades and luckily sending the data back information can travel at the speed of light so that would only take another four years once they managed to fly by so yeah even with the most wildly optimistic Pie in the Sky dreaming idea we are not going to be able to visit our neighbors and anytime soon but even so it is just so damn exciting that we have exo planets so close to us especially one that is potentially habitable I just honestly feel so lucky to be alive at a time that we can know these kind of things and I really look forward to all the future information we're going to learn about the exit planets next door [Music]