Astronomy

Can tidal forces cause an exoplanet’s surface to radiate heat? This is what a recent study accepted to The Astronomical Journal hopes to address as a team of international researchers used data collected from ground-based instruments to confirm the existence of a second exoplanet residing within the exoplanetary system, HD 104067, along with using NASA’s Transiting Exoplanet Survey Satellite (TESS) mission to identify an additional exoplanet candidate, as well. What’s unique about this exoplanet candidate, which orbits innermost compared to the other two, is that the tidal forces exhibited from the outer two exoplanets are potentially causing the candidates’ surface to radiate with its surface temperature reaching as high as 2,300 degrees Celsius (4,200 degrees Fahrenheit), which the researchers refer to as a “perfect tidal storm”.

Here, Universe Today discusses this fantastic research with Dr. Stephen Kane, who is a Professor of Planetary Astrophysics at UC Riverside and lead author of the study, regarding the motivation behind the study, significant results, the significance of the “tidal storm” aspects, follow-up research, and implications for this system on studying other exoplanetary systems. So, what was the motivation behind this study?

“The star (HD 104067) was a star known to harbor a giant planet in a 55-day orbit, and I have a long history of obsessing over known systems,” Dr. Kane tells Universe Today. “When TESS detected a possible transiting Earth-size planet in a 2.2-day orbit (TOI-6713.01), I decided to examine the system further. We gathered all RV data and found that there is ANOTHER (Uranus mass) planet in a 13-day orbit. So, it started with the TESS data, then the system just kept getting more interesting the more we studied it.”

Dr. Kane’s history of exoplanetary research encompasses a myriad of solar system architectures, specifically those containing highly eccentric exoplanets, but also includes follow-up work after exoplanets are confirmed within a system. Most recently, he was the second author on a study discussing a revised system architecture in the HD 134606 system, along with discovering two new Super-Earths within that system, as well.

For this most recent study, Dr. Kane and his colleagues used data from the High Accuracy Radial velocity Planet Searcher (HARPS) and High Resolution Echelle Spectrometer (HIRES) ground-based instruments and the aforementioned TESS mission to ascertain the characteristics and parameters of both the parent star, HD 105067, and the corresponding exoplanets orbiting it. But, aside from discovering additional exoplanets within the system, as Dr. Kane mentions, what are the most significant results from this study?

Dr. Kane tells Universe Today, “The most amazing outcome of our work was that the dynamics of the system causes the 2.2-day period to experience enormous tidal effects, similar to those experienced by Io. In this case though, TOI-6713.01 experiences 10 million times more tidal energy than Io, resulting in a 2600K [2,300 degrees Celsius (4,200 degrees Fahrenheit)] surface temperature. This means the planet literally glows at optical wavelengths.”

Jupiter’s moon, Io, is the most volcanically active planetary body in the solar system, which is produced from tidal heating caused by Jupiter’s massive gravity throughout Io’s slightly eccentric (elongated) orbit lasting 1.77 days. This means that Io gets closer to Jupiter during certain points and farther away from Jupiter at other points causing Io to compress and expand, respectively. Over millions of years, this constant friction within Io’s interior has led to the heating of its core, resulting in the hundreds of volcanoes that comprise Io’s surface and no visible impact craters, as well. As Dr. Kane mentions, this new exoplanet candidate “experiences 10 million times more tidal energy than Io”, which could raise additional questions regarding its own volcanic activity or other geologic processes. Therefore, what is the significance of the “tidal storm” aspects of TOI-6713.01?

Dr. Kane tells Universe Today, “The reason TOI-6713.01 experiences such strong tidal forces is because of the eccentricity of the outer two giant planets, forcing TOI-6713.01 into an eccentric orbit also. Thus, I referred to the planet as being caught in a perfect tidal storm.”

The HD 104067 system with its two outer giant exoplanets forcing the innermost TOI-6713.01 into a “perfect tidal storm” is slightly reminiscent of Jupiter’s first three Galilean moons, Io, Europa, and Ganymede, regarding their gravitational effects on each other throughout their orbits. There are some differences, however, since Jupiter’s massive gravity is the primary force driving Io’s volcanic activity, and all three moons are in what’s known as orbital resonance, which means the orbits are ratioed with each other. For example, for every four orbits of Io there are two orbits of Europa and one orbit of Ganymede, making their orbital resonance 4:2:1, which results in each moon causing regular gravitational influences on each other. Therefore, with the tidal storm aspect on TOI-6713.01 being caused by the eccentricities of the two outer giants, how does this compare to the relationship between Io, Europa, and Ganymede?

Dr. Kane tells Universe Today, “The Laplace resonance of the Galilean moons creates a particularly powerful configuration, whereby regular alignments of the inner three moons regularly force Io into an eccentric orbit. The HD 104067 system is not in resonance but is still able to produce a power configuration by virtue of the b and c planets being so massive and is therefore more of a “brute force” effect of forcing the inner transiting planet into an eccentric orbit.”

As noted, TOI-6713.01 was discovered using the radial velocity method, also known as Doppler spectroscopy, meaning astronomers measured the miniscule changes in the movement of the parent star as it’s slightly tugged by the planet during the latter’s orbit. These slight changes cause the parent star to wobble as the two bodies tug on each other, and astronomers use a spectrograph to detect changes in these wobbles as the star moves “closer” and “farther away” from us to find exoplanets. This method has proven to be very effective in finding exoplanets, as it accounts for almost 20 percent of the total confirmed exoplanets to date, and the first exoplanet orbiting a star like our own was discovered using this method, as well. However, despite the effectiveness of radial velocity, the study notes how TOI-6713.01 “has yet to be confirmed”, so what additional observations are required to confirm its existence?

Dr. Kanes tells Universe Today, “Because the planet is so small, it’s difficult to detect it from the radial velocity data. However, the transits look clean, and we have ruled out stellar contamination. Additional transits will help, but we’re quite confident in the existence of the planet at this point.”

This study comes as the total number of exoplanetary systems is almost 4,200 with the number of confirmed exoplanets exceeding 5,600 and more than 10,100 exoplanet candidates waiting to hopefully be confirmed, as well. These system architectures have been found to vary widely from our own solar system, which is comprised of the terrestrial (rocky) planets closer to the Sun and the gas giants orbiting much farther out. Examples include hot Jupiters that orbit dangerously close to their parent star, some in only a few days, and other systems boasting seven Earth-sized exoplanets, some of which orbit within the habitable zone. Therefore, what can this unique solar system architecture teach us about exoplanetary systems, overall, and what other exoplanetary systems mirror it?

Dr. Kane tells Universe Today, “This system is a great example of extreme environments that planets can find themselves in. There have been several cases of terrestrial planets that are close to their star and heated by the energy from the star, but very few cases where the tidal energy is melting the planet from within.”

The potential discovery of an exoplanet orbiting in a “perfect tidal storm” further demonstrates the myriad of characteristics that exoplanets and exoplanetary systems exhibit while contrasting with both our own solar system and what astronomers have learned about them until now. If confirmed, TOI-6713.01 will continue to mold our understanding regarding the formation and evolution of exoplanets and exoplanetary systems throughout not only our Milky Way Galaxy, but throughout the cosmos, as well.

“The universe is an amazing place!” Dr. Kane tells Universe Today. “The fun thing about this particular project is that it all started with ‘Hmm … this might be interesting’ then turned into something far more fascinating than I could have imagined! Just goes to show, never miss the chance to follow your curiosity.”

How will this tidal storm exoplanet teach us about other exoplanets and exoplanetary systems in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

The post Radiating Exoplanet Discovered in “Perfect Tidal Storm” appeared first on Universe Today.

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Untangling what happened in our Solar System tens or hundreds of millions of years ago is challenging. Millions of objects of wildly different masses interacted for billions of years, seeking natural stability. But its history—including the migration of the giant planets—explains what we see today in our Solar System and maybe in other, distant solar systems.

New research shows that giant planet migration began shortly after the Solar System formed.

Planetary migration is a well-established idea. The Grand-Tack Hypothesis says that Jupiter formed at 3.5 AU, migrated inward to 1.5 AU, and then back out again to 5.2 AU, where it resides today. Saturn was involved, too. Migration can also explain the Hot Jupiters we see orbiting extremely close to their stars in other solar systems. They couldn’t have formed there, so they must have migrated there. Even rocky planets can migrate early in a solar system’s history.

New research in the journal Science establishes dates for giant planet migration in our Solar System. Its title is “Dating the Solar System’s giant planet orbital instability using enstatite meteorites.” The lead author is Dr. Chrysa Avdellidou from the University of Leicester’s School of Physics and Astronomy.

“The question is, when did it happen?” Dr. Avdellidou asked. “The orbits of these planets destabilised due to some dynamical processes and then took their final positions that we see today. Each timing has a different implication, and it has been a great matter of debate in the community.”

“What we have tried to do with this work is to not only do a pure dynamical study, but combine different types of studies, linking observations, dynamical simulations, and studies of meteorites.”

The meteorites in this study are enstatites or E-type asteroids. E-type asteroids have enstatite (MgSiO3) achondrite surfaces. Achondrite means they lack chondrules, grains of rock that were once molten before being accreted to their parent body. Specifically, this group of meteorites are the low-iron chondrites called ELs.

When giant planets move, everything else responds. Tiny asteroids are insignificant compared to Jupiter’s mass. Scientists think E-type asteroids were dispersed during the gas giants’ outward migration. They may even have been the impactors in the hypothetical Late Heavy Bombardment.

Artist concept of Earth during the Late Heavy Bombardment period. Scientists have wondered if E-type asteroids disturbed during giant planet migration could’ve been responsible for the Bombardment, but the authors of this research don’t favour that explanation. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab.

Enstatite achondrites that have struck Earth have similar compositions and isotope ratios as Earth. This signals that they formed in the same part of the protoplanetary disk around the young Sun. Previous research by Dr. Avdellidou and others has linked the meteorites to a population of fragments in the asteroid belt named Athor.

This work hinges on linking meteorites to parent asteroids and measuring the isotopic ratios.

“If a meteorite type can be linked to a specific parent asteroid, it provides insight into the asteroid’s composition, time of formation, temperature evolution, and original size,” the authors explain. When it comes to composition, isotopic abundances are particularly important. Different isotopes decay at different rates, so analyzing their ratio tells researchers when each meteorite closed, meaning when it became cool enough that there was no more significant diffusion of isotopes. “Therefore, thermochronometers in meteorites can constrain the epoch at which major collisional events disturbed the cooling curves of the parent asteroid,” the authors explain.

The team’s research shows that Athor is a part of a once much larger parent body that formed closer to the Sun. It also suffered from a collision that reduced its size out of the asteroid belt.

Athor found its way back when the giant planets migrated. Athor was at the mercy of all that shifting mass and underwent its own migration back into the asteroid belt. Analysis of the meteorites showed that this couldn’t have happened earlier than 60 million years ago. Other research into asteroids in Jupiter’s orbit showed it couldn’t have happened later than 100 million years ago. Since the Solar System formed about 4.56 billion years ago, the giant planet migration happened between 4.5 and 4.46 billion years ago.

This schematic from the research shows what the researchers think happened. Red circles are planetesimals (and their fragments) from the terrestrial planet region. The black solid curves roughly denote the boundary of the current asteroid inner main belt. Eccentricity increases from bottom to top.

A shows the formation and cooling of the EL parent planetesimal in the terrestrial planet region before 60 Myr after Solar System formation. In this period, the terrestrial planets began scattering planetesimals to orbits with high eccentricity and semimajor axes corresponding to the asteroid main belt. B shows that between 60 and 100 Myr, the EL planetesimal was destroyed by an impact in the terrestrial planet region. At least one fragment (the Athor family progenitor) was scattered by the terrestrial planets into the scattered disk, as in (A). Then the giant planet instability implanted it into the inner main belt by decreasing its eccentricity. C shows that a few tens of millions of years after the giant planet instability occurred, a giant impact between the planetary embryo Theia and proto-Earth formed the Moon. D shows that the Athor family progenitor experienced another impact event that formed the Athor family at ~1500 Myr. Image Credit: Avdellidou et al. 2024.

Another important event happened right around the same time. About 4.5 billion years ago, a protoplanet named Theia smashed into Earth, creating the Moon. Could it all be related?

“The formation of the Moon also occurred within the range that we determined for the giant planet instability,” the authors write in their research. “This might be a coincidence, or there might be a causal relationship between the two events.”

“It’s like you have a puzzle, you understand that something should have happened, and you try to put events in the correct order to make the picture that you see today,” Dr. Avdellidou said. “The novelty with the study is that we are not only doing pure dynamical simulations, or only experiments, or only telescopic observations.”

“There were once five inner planets in our Solar System and not four, so that could have implications for other things, like how we form habitable planets. Questions like, when exactly objects came delivering volatile and organics to our planet to Earth and Mars?”

Artist’s impression of the impact that caused the formation of the Moon. Could giant planet migration have caused that impact? Credit: NASA/GSFC

The Solar System’s history is a convoluted, beautiful puzzle that somehow led to us. Everything had to work out for life to arise on Earth, sustain itself, and evolve for so long. The epic migration of the gas giants must have played a role, and this research brings its role into focus.

Never mind habitability, complex life, and civilization, the migration may have allowed Earth to form in the first place.

“The timing is very important because our Solar System at the beginning was populated by a lot of planetesimals,” said study co-author Marco Delbo, Director of Research at France’s Nice Observatory. “And the instability clears them, so if that happens 10 million years after the beginning of the Solar System, you clear the planetesimals immediately, whereas if you do it after 60 million years you have more time to bring materials to Earth and Mars.”

The post The Giant Planets Migrated Between 60-100 Million Years After the Solar System Formed appeared first on Universe Today.