Astronomer Anthony Boccaletti discusses observation of birth of potential exoplanet with Wikinews
Tuesday, July 7, 2020
In March, a study conducted by astronomer Anthony Boccaletti and other researchers reported potential signs of formation of an exoplanet around the star AB Aurigae. Exoplanets are those planets which are outside the Solar System.
The host star AB Aurigae is a young star, roughly five million years old, Boccaletti told Wikinews. In contrast, the Sun is approximately 4.6 billion years old. Located in the Auriga constellation, AB Aurigae is about 520 light years away from the Earth. The astronomers observed the protoplanetary disk around the star.
Image: acagastya.
The astronomers used the European Southern Observatory's Very Large Telescopes in Chile to study this system. Boccaletti told Wikinews the twists they saw in the protoplanetary disk of gas and dust could be the formation of either a humongous planet, bigger than Jupiter, the largest planet in the Solar System; or it could less likely be a star, or a brown dwarf.
The disturbance in the twist is located around 30 astronomical units — one astronomical unit is the distance between the Sun and the Earth — from the host star. That is almost the distance from the Sun to Neptune. However, the host star AB Aurigae is more massive than the Sun: about 2.4 times the mass of the Sun. AB Aurigae is classified as a Herbig Ae star, which are known for their brightness.
Boccaletti and his team started observing the system in 2019. Boccaletti said the researchers would like to follow up the study to confirm the observed twists are indeed the birth of an exoplanet. "[I]f we confirm that it's a planet in formation then it becomes very important to follow up", he said.
There exists multiple theories of exoplanet formation, however, the formation of an exoplanet has never been observed till date. Discovered in 2016, K2-33b is one of the youngest exoplanets known so far, and it is about 9.3 million years old.
Boccaletti, who works at the Observatoire de Paris, discussed his findings with Wikinews last month.
Interview with Anthony Boccaletti
Thank you for agreeing to discuss your findings on formation of exoplanets. I would like to discuss the study, and the inferences; as well as what lies ahead to be studied.
((WN
)) What prompted your interest in astronomy?
((Anthony Boccaletti)) Why I am interested in astronomy?
((WN)) Yeah.
((Anthony Boccaletti)) Uhh... [laughs] because it's fun. [laughs] Because it's — it's about objects that are very far from us, and which we never observed before. So it's always very challenging to understand astrophysical objects which are very distant from us; and very different from what we see in the Solar System, for instance.
((WN)) How did you get involved with this study?
((Anthony Boccaletti)) I was involved because I also took part in the building of the instrument. So the instrument that we used at the Very Large Telescope; instrument is a SPHERE [Spectro-Polarimetric High-Contrast Exoplanet Research]. And so we started the design of the instruments back in 2005, I would say. So I was involve[d] already at this step. And then when the instrument was implemented on the sky, on the telescope, I was also involved in the survey, that was accomplished with this telescope. And, in addition to the survey — in addition to all the observations that the consortium of people who built the instrument was running — I also had my own programs with other colleagues. And this result is part of these other programs.
((WN)) Was this instrument built specifically for this research?
((Anthony Boccaletti)) It was built for imaging exoplanets and also planetary systems.
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((WN)) What drew your attention to AB Aurigae in the Auriga constellation in the first place?
((Anthony Boccaletti)) Well it's because it was already observed before, of course, so we knew that there was a protoplanetary disc around the star. And the most recent images were obtained with Alma: the Atacama Large Millimeter Array. It's an interferometer working in Radio astronomy. And from this telescope, we already had a suspicion that there might be a planet in formation in this disc. And this is why we decided to use SPHERE to observe this system.
((WN)) Could you explain this study and its findings?
((Anthony Boccaletti)) Yes so: so AB Aurigae is a star which is more massive than the Sun, but also very very young. The Sun is like 4.5 billion years old; while AB Aurigae is probably only like 5 million years old. So very young. And around young stars, we expect planets could be very bright because we are observing in the infrared. And so we knew that there was a protoplanetary disc around AB Aurigae. That means a system with a lot of gas, and a lot of dust. And so when we see this, you can find out that this gas and this dust will evolve into planets. So this is what we focused on. We decided to observe with SPHERE in order to observe the very details in the protoplanetary system of AB Aurigae and try to identify if there was [a] planet in the system. And so what we find is that we have a lot of structures. And we call these spirals because they have spiral shapes and these spirals are in fact gas, which are taking this shape. And usually, when we see a spiral, we can infer that there is an object which is perturbating the gas. The gravitation impact of an object in the gas produces a spiral. So when you see a spiral in a disk, you try to find which object has triggered the spiral. Because you know that it's produced by an instability. So this instability could be anything, but it could be also [a] planet: [a] planet in formation. So we try to identify if some of these pattern[s], structures in the disk could be related to the presence of a planet. And so, when we get the images from SPHERE, we find that one of the spiral[s] was twisted. And it's not a perfect spiral, you have a kind of structure at the tip of one of the spirals, which looks like a twist. Like if the spiral was twisted. And this is exactly what we expect from modelisation, from theory of planet formation. When you ask people doing modelling, what looks like a system in which a planet is forming, and if you have gas in this system, what the image looks like, and they will give you an image which resembles a lot what we observe in AB Aurigae. So we did not observe a planet, okay? We never detect[ed] a planet. We detect[ed] a structure which could be the impact of a planet on to the gas. On to this spiral. So this is indirect: indirect
detection.
The other problem is that we don't know which mass is creating this structure, this spiral. So we see the spiral, we see the structure, we have theories indicating that it could be [a] planet. But we are not able to measure the mass of the object. So, we concluded that it could be a planet, but it could be also something more massive than a planet. Like maybe a brown dwarf for instance, an object a little bit more massive than a planet. So it's still a study that is ongoing. We are continuing the observations in order to determine if this is actually a planet in formation, or if it is another type of object.
((WN)) What was the timeline of the study?
((Anthony Boccaletti)) Oh, the timeline was typically we started by asking telescope-time. So, requesting telescope-time like a year
ago; last year, basically. The request for observing time was accepted. And then, the observation were executed in December 2019. Last year.
((WN)) Were you initially looking for signs of formation of an exoplanet specifically?
((Anthony Boccaletti)) Yes, definitely. This is exactly why we are observing very young star. Because we know that the planets are forming when a star is very young; so when it's like one million or five million years old. And it took about probably a million year for a planet to form. So it is important to look at very young planet, if you want to understand how the planet forms, you need to look at very young systems.
((WN)) How many countries were involved in the study?
((Anthony Boccaletti)) Countries! Oh, so we have some people from France, people from US, people from Taiwan, and people from Belgium. So we have four countries.
((WN)) And how many people were involved in this study?
((Anthony Boccaletti)) Let me check exactly the number of people if I can. I think we were like ten people? I can check directly. There are one, two, three [counts]. We are eleven people.
((WN)) And what are their roles?
((Anthony Boccaletti)) Oh, the roles of the other people? Okay, so the other people contributed to the interpretation of the data, mostly. So once we have done the observation, we need to understand what we are observing. So we need to compare the observation with models for instance. So, a lot of people contributed to this comparison. Some people contributed to making a link with the previous data we have with ALMA. And that's basically the role of the other people. And some of them also contributed to the writing of the paper.
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((WN)) From which observatory were the observations made?
((Anthony Boccaletti)) They were made from the Very Large Telescope in Chile.
((WN)) Which activity took the most time and attention?
((Anthony Boccaletti)) That's a good point. [laughs] I think it's definitely the last: the last phase, of writing the paper.
((WN)) And what was the most difficult part of this investigation?
((Anthony Boccaletti)) Well the most difficult was to be convinced that we are actually looking at something which is very new, so we need to convince ourselves that it's valuable for scientific publication. It's not specifically hard, but it requires to be convinced, so to make sure that you have done the analysis correctly. You don't make any mistake, et cetera.
((WN)) What was your first reaction when you concluded it is likely to be the formation of an exoplanet?
((Anthony Boccaletti)) I think it was very exciting, even though we don't have an image of an exoplanet directly. Having even a suspicion that it could be a planet-forming, since it is very new; it was very exciting.
((WN)) What was the most fascinating aspect of this study?
((Anthony Boccaletti)) Well again it's about the same question but, I think it gives it gives some perspective in the work. So it's a system for which we will re-observe, ask more telescope time to perform more observation, because if we confirm that it's a planet in formation then it becomes very important to follow up. So to monitor the system, make sure that it's a planet, make sure that it rotates around the star, et cetera.
((WN)) What were some of the challenges the team faced during the study?
((Anthony Boccaletti)) The challenges?
((WN)) Yes.
((Anthony Boccaletti)) Um. Well the challenges [are]: first, to get very good observation; and, well you know, when you observe at the telescope, sometimes the conditions are good, sometimes they are not so good. And I think we were very lucky to have very good — extremely good condition, in fact. So the fact that we see very clearly something is also related to the quality of the data, the quality of the telescope, of the instruments. So that's the first challenge to get the data with a very good quality. And then the second challenge is to compare the observation with the models. Because there are many models. Some are more or less complex. Some are very detailed. Some are less detailed. And you have to figure out which one is the most appropriate for the comparison. Because you don't want to make an interpretation that is too far. You don't want to conclude something that is not very correct. So you need also to make sure that you use the right model. And so, you use one of the models that exists. It's not the most sophisticated. It's the one, on the opposite, which is almost the simplest. Because it's enough to interpret the images, in fact. So now, of course we need to think about models that are more detailed in order to explain the observations.
((WN)) Which technologies were used on this study?
((Anthony Boccaletti)) So we use a technology called adaptive optics which is something which is integrated into the instrument which is able to correct for the atmospheric turbulence. So, when the light from the star cross[es] the atmosphere of the Earth, it becomes blurred. And we are correcting this blurring in order to have very very fine detail on the images. So that's one of the one of the technolog[ies] we are using.
The second one is coronagraphy. So exactly like a system which is able to observe the Sun Corona. So you block: when you block the Sun and you try to see around the Sun, well it's the same sort of technology but applied to stars instead of the Sun. So all the stars — and so the stars are much smaller — and this system is able to block the light from the star, so you can see everywhere around, and look for planets, look for discs, look for structures. These are the two main technologies we used.
((WN)) Why were these two technologies ideal for this study?
((Anthony Boccaletti)) Oh, um yeah, it's not the only ones but yeah, they are necessary to perform this study, definitely. Yeah.
((WN)) What makes this study unique?
((Anthony Boccaletti)) Well, it's not unique because we have already many observation of planetary systems. We have a lot of observation of disks — protoplanetary disks — and especially SPHERE has observed a lot of them. We also have images of planets. And we know that planet are forming inside disks: inside protoplanetary disks. And we know that planet should generate structures like spirals in a disk. So we knew from the theory that planet and spirals are connected, but we never ever made the connection between the two. So we never observed in the same system a planet and the spiral, ok. So here, we don't have exactly observed that because we did not detect the planet, but we detected the presence of the planet in the structure of the spiral. So we are getting one step closer to making the connection between the planet and the spirals, and the structures in the disk.
((WN)) What is currently the best explanation for the formation of exoplanets?
((Anthony Boccaletti)) There are several scenarios for forming exoplanets and we have only — we never witness planet formation, so we only have theories, which are based on a lot of observations, of course, including observations of the Solar System, planet in the Solar System, et cetera. The analysis of rocks on the Earth as well in the Solar System. But we [have] never seen a planet forming. So, there are several theories. One of them is that you have rocks forming into the system. And these rocks are colliding, they are making bigger rocks. Bigger and bigger. And when this rock has reached a mass which is large enough, like maybe ten times the mass of the Earth, then this big rock, this big planet, starts to accrete the gas. And it becomes a giant planet like Jupiter or Saturn. So that's the theory for forming a giant planet.
There are other way to form telluric planet, rocky planet, like the Earth. But here, in fact, the [case] we were talking about — if it is a planet, it's necessarily a planet that is big like Jupiter, or maybe even bigger. So we believe that the planet form first: the rock of the core of the planet is forming first. And when the core is formed, then it accretes the gas, which literally falls on the core of the planet, and it makes a bigger planet: which is a gas giant planet.
((WN)) So what kind of exoplanet will this be if this planet forms?
((Anthony Boccaletti)) It will be a giant planet, really. Maybe even bigger than Jupiter. Maybe 10 times the mass of Jupiter. But it couldn't be a planet that is like the Earth. If it were a planet like the Earth, it wouldn't make this kind of spiral. The spiral would not be detectable, in that case. So it's necessarily a very big planet.
((WN)) So, is it safe to conclude that it could be a hot Jupiter?
((Anthony Boccaletti)) No, it's not a hot Jupiter. Because, well hot Jupiter means two different type[s] of planets. Jupiter can be hot if it is very close to the star. And this is usually what we refer when we say hot Jupiter. But, when a planet like Jupiter is forming, then the temperature is very high. It's like one thousand, maybe two thousand degrees. So, it's also a hot Jupiter. But not because it's close to the star: because it's young, okay. So here, we are talking about a young Jupiter planet which is probably very warm.
((WN)) What do we know about the planetary system that is being formed?
((Anthony Boccaletti)) Well we don't know much, in fact. [laughs] We know we know a little bit about the edge of the system. We know the quantity of gas and dust that is there, and which will form planets anyway. But we don't know yet how many planets are formed; if this planet will survive, et cetera. So there's still a lot to be understood about this system.
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((WN)) Why do you think this planet may not survive? [...] As you mentioned we do not know if this planet is going to survive.
((Anthony Boccaletti)) Yeah, because some planets: some planet form in the disk, okay. If you have a planet forming in the disk, then the disk is made of gas. And when the planet rotate[s] around the star, then there is a friction with the gas. And so the planet slow[s] down. And when it slow[s] down, it gets closer to the star. And eventually, it can be a hot Jupiter. And sometimes, it can even disappear into the star: swallowed by the star. So we know that some planets are forming in systems and they finally end up merging with the star. They disappear
into the star. So we don't know if all planets survive, in fact. Well this one is probably like 30 astronomical units [an astronomical unit is the distance from the Sun to the Earth, about 150 million km; 93 million miles] away from the star. So it's very far away. There's not a lot of change for this planet to migrate very close and disappear in the star. But we know that it can happen.
((WN)) Could you tell us more about the host star?
((Anthony Boccaletti)) The star is more massive than the Sun. It's 2.4 times the mass of the Sun [mass of Sun = about 2×1030 kg]. It's also very young, as I said, only a few million years. Yeah. Essentially that's the two parameters.
((WN)) And what do we know about the history of the system?
((Anthony Boccaletti)) Not much. [laugh] Unfortunately, not much. No. We don't even have an exact measurement of the age. Because it can be between like one and five million years old. So it's not very accurate.
((WN)) This host star is a Herbig Ae star, right?
((Anthony Boccaletti)) Yeah, yeah.
((WN)) What are some of the typical characteristics of a Herbig Ae star?
((Anthony Boccaletti)) They are very bright. Because they are very massive, so it's essentially the mass of the star which makes it an Herbig star. And they have also a lot of emissions. So, when we started observing star with spectrograph, we realised that it had signatures in the spectrum, and in fact, the reason why they have signature is because they have an environment of gas. So, the light from the star is traveling through the gas, and creates some absorption, or emission in some cases. And we see this is a signature in the spectrum. So, the fact that it's a Herbig Ae star means in fact, that it is surrounded by a disk.
((WN)) How common are these stars?
((Anthony Boccaletti)) Oh, I don't have a clear idea of that. [laughs] [I] cannot answer.
((WN)) And how often do Herbig stars have orbiting planets?
((Anthony Boccaletti)) I don't know if we have already example. I don't think we have many example[s] of planets around the Herbig Ae star. It could be it could be one of the first, in fact, yeah. Not many.
((WN)) As you mentioned, the spot formation of this potential planet is quite far from the host star — 30 astronomical units — what does the distance between this spiral and the star tell us?
((Anthony Boccaletti)) Well it tells us that planet[s] can form at 30 astronomical units. That's already: I mean if it is really a planet in formation then it forms at 30 astronomical unit. Which is not of use, in fact. And, in fact, we never, as I said before, we never witnessed a planet at formation. So it tells us that really, a planet can form at such a distance from the star. In the Solar System, 30 astronomical unit is very far. It's the orbit of Neptune. But this one is not the Solar System; it's not the Sun. It's more massive than the Sun. So, 30 astronomical units — it's far away, but not not as far as in the Solar System, okay. But at least we see that it's possible to form as a planet at this position.
((WN)) In what ways will this distance affect the planet formation?
((Anthony Boccaletti)) I don't know. Well, we don't have a clear idea of that.
((WN)) Were there any unique traits in the orbit of the system?
((Anthony Boccaletti)) The orbit? No. Well we don't have the orbit yet. I mean, we just have an image, and we don't have the full orbit yet. So, we don't really know yet what is the orbit.
((WN)) When did you first consider the possibility of it being a birth of an exoplanet, rather than being something else?
((Anthony Boccaletti)) Well, as I said it's when we started to realise that the image was very similar to the models. So, it's a suspicion that it should be a planet forming. Although it's not a firm conclusion, of course.
((WN)) What other plausible hypothesis of what this twist might be?
((Anthony Boccaletti)) It could be a more massive object. It could be a brown dwarf. It could be a star also; it's unlikely, but it could be a star. It could be also just what we call instabilities in a system. So not always related to planets. But other sort of instability. A planet is somehow an instability because, while it rotates in the disk of gas, it disrupts the disk, the gas and create an instability. But an instability can arise also for other reasons than a planet.
((WN)) And how do they rule out the other possibilities?
((Anthony Boccaletti)) Well, we're not completely ruling out the other possibilities. If it were a star, it should have been visible as a star. So, we believe it's not a star. Well, at least it's not likely. And this is why we believe it should be a planet. Something that we don't see directly. We don't detect it.
((WN)) Is there a possibility this system might form multiple exoplanets?
((Anthony Boccaletti)) Yes, definitely. Definitely. Because we see a lot of spirals. And if each of the spiral was actually a planet, then that means a lot of planets. So in principle, when a system from one planet, there is no reason for not forming other planets.
((WN)) And how many exoplanets are we talking about?
((Anthony Boccaletti)) Oh, we don't know. [laughs] We don't know at all.
((WN)) What does the analysis of radiation emission spectrum of the system reveal?
((Anthony Boccaletti)) In fact it's difficult, because it's not straightforward to measure the emission because of the disk. So the disk has a lot of structures and so it's difficult to measure the flux from the planet. And in fact, we believe that we are not able to detect the flux of the planet. And this is why we conclude that we don't see the planet. So we see only the flux from the gas and the dust in the system, but not from the planet directly.
((WN)) What do we know about the composition of the dust and gas in the spiral?
((Anthony Boccaletti)) Well, we know that there are molecules in this system; like carbon monoxide, for instance. Certainly also a lot of hydrogen, of course. And for the dust, it can be any kind of dust because we don't have very strong constraints. So in fact, the dust that we see with SPHERE is different than the dust that we will see with another telescope, because we are not using the same spectral range. So with SPHERE's near-infrared we are sensitive to dust that have sizes of a few microns [1 micron = 0.001 mm] — little grains — and we don't see the other big grains, in fact. It doesn't mean that they are not there. It means that we don't have the sensitivity to see it. So there's a whole distribution of dust; dust sizes.
((WN)) What kind of atmosphere will this potential planet [be] likely to have in future?
((Anthony Boccaletti)) Well certainly a gas planet; so with an atmosphere of hydrogen and helium, in majority.
((WN)) How many spirals were observed?
((Anthony Boccaletti)) So in the central part we see at least two big spirals. But in fact, all these spirals have little structures, so we see a lot of them. But mostly in the very inner part. And then, if you look at the very outer part, then you see a lot of a lot more spirals. But we believe that these ones are not due to planets, but more to instabilities.
((WN)) Were these two spirals interfering?
((Anthony Boccaletti)) Um, yes, probably! Probably. Yeah, if you have more planets in the system, then they all launch spirals. And all of them interfere.
((WN)) How big were these spirals?
((Anthony Boccaletti)) How big? They can be several several hundreds of astronomical units.
((WN)) What does the next few million years for this system look like?
((Anthony Boccaletti)) Probably that in one million year the planet will be formed. And most of the gas will be dissipated. So, all the disk we see in the image will disappear and we will be left with planets. Or maybe it will take more than one million year. Maybe five or ten. That's the point. We don't know exactly.
((WN)) If that is the case this will make it the youngest discovered exoplanet so far, right?
((Anthony Boccaletti)) Yes, if it is an exoplanet, then it's the youngest, yeah.
((WN)) When do astronomers use near-infrared imaging of the stars?
((Anthony Boccaletti)) Well we use an infrared because it's the wavelength where we can use adaptive optics also. So with adaptive optics, we can provide very detailed images. And we need to resolve the very central part of system so we need adaptive optics. So near-infrared is interesting because you can use adaptive optics, and also because it's the range where you expect a planet to be very bright. If you look in the visible [light range], the planet will be very faint.
((WN)) How do you test your hypothesis?
((Anthony Boccaletti)) How do we test the hypothesis? Of what — Of the planet? Of the object being the planet?
((WN)) Yes.
((Anthony Boccaletti)) Well, again I think it's: at the moment the only test is to compare with the models. That's the only thing we can do.
((WN)) What is your role at the Observatoire de Paris?
((Anthony Boccaletti)) I'm a researcher. And I work on exoplanets and protoplanetary disks. Yeah, mostly I work also on design of instruments. I'm doing instrumentation and observations and interpretation of observations.
((WN)) Is your team planning to study more about this system?
((Anthony Boccaletti)) Yes definitely. We already asked for more telescope time to re-observe AB Aurigae.
((WN)) And what do you expect to find about the system this time?
((Anthony Boccaletti)) We would like to confirm first that the structure is still visible. To see if it rotates around the star in a Keplerian motion. And if the the shape of the spiral is stable or evolve[s] over time.
((WN)) What lies ahead to be discovered about exoplanets?
((Anthony Boccaletti)) A lot of things. [laughs] Many many many things, yeah. [laughs] It will be too long to describe what has to be done on exoplanets. It's really a young science. So, in particular, we need to understand how they form. And what they are made of, also.
((WN)) Are we be likely to find more instances of planet formation in the near future?
((Anthony Boccaletti)) Yeah, yes. Definitely. We've instruments like SPHERE or GPI [Gemini Planet Imager] or other instruments that are installed on 8-meter telescopes. Also with the next Space Telescope, James Webb, you will find out more planets. The next big telescope on the Earth will be the extremely large telescope which is a 38-meter telescope. So also we expect to find more planets.
((WN)) How can this discovery influence what we already know about planet formation?
((Anthony Boccaletti)) Again I think it's really because it's a very young system. So we never really observe this stage with SPHERE. We have done that with ALMA — with the instrument ALMA — we can observe very young system, but we don't see the same thing. We see mostly big dust, and gas. But with SPHERE, it's really new to be interested in very very young stars.
((WN)) What do we now know about planet formation that we didn't know before?
((Anthony Boccaletti)) What we learn is typically that a planet could form at 30 astronomical unit from a star, that is more massive than the Sun. And that it has an impact on the distribution of the gas and the dust. That's mostly what we learned. And of course, this system is a cornerstone, and we'll probably observe more systems like AB Aurigae in the future.
((WN)) What are some of the other studies you are currently working on?
((Anthony Boccaletti)) That's typically on other systems that are a bit older than AB Aurigae, in fact. Usually the stars we are observing with SPHERE are like 10 or 20 million years old. It's basically — less than 50 million years old. Between 10 and 50, say, million years. And they have gas and dust around, so we can detect discs. And so we are performing a survey of hundreds of stars to detect new planets.
((WN)) Well, those were all the questions I had for you. Would you like to add anything?
((Anthony Boccaletti)) No. I think we we already covered the subject very much. Thank you for your questions.
((WN)) Thank you for agreeing for this interview. It has been a great pleasure discussing this with you.
((Anthony Boccaletti)) Oh, me too. Thank you very much.
Sister links
Sources
- "Jupiter" — NASA, June 8, 2020 (date of access)
- "ESO Telescope Sees Signs of Planet Birth" — European Southern Observatory, May 20, 2020
- A. Boccaletti , E. Di Folco , E. Pantin , A. Dutrey , S. Guilloteau , Y. W. Tang , V. Piétu , E. Habart , J. Milli , T. L. Beck , and A.-L. Maire. "Are we witnessing ongoing planet formation in AB Aurigae?" — Astronomy & Astrophysics, March 23, 2020
- "Exoplanet Orbits Youthful Star (Artist's Concept)" — NASA, June 20, 2016
- "k2-33 b" — CalTech, July 4, 2020 (date of access)
