Can We Predict if a System Will Have Giant Planets?

Prediction is one of the hallmarks of scientific endeavors. Scientists pride themselves on being able to predict physical realities based on inputs. So it should come as no surprise that a team of scientists at Notre Dame has developed a theory that can be used to predict the existence of giant planets on the fringes of an exoplanetary system.

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Sci-Fi Christmas is Ruined! Planet Vulcan Doesn’t Exist

Fans of Star Trek were over the Moon when, in 2018, astronomers with the Dharma Planet Survey (DPS) announced the possible detection of 40 Eridani b, an extrasolar planet in the star system 40 Eridani. Located just 16.3 light-years away, this triple-star system happens to be where the planet Vulcan was located in the popular franchise. Based on radial velocity measurements of the system’s primary star (40 Eridani A), the discovery team estimated that “Vulcan” was a rocky planet several times the mass of Earth (a Super-Earth) with an orbital period of 42 days or so.

The existence of this exoplanet has remained a controversial subject ever since. A study released in 2021 concluded that the signal was a false positive, but the debate remained open. Now, according to a new study by an international team of researchers, the detection of 40 Eridani b was a false positive that astronomers mistook for an exoplanet. The study was part of an archival review of exoplanets to identify promising candidates for follow-up studies. So while “Vulcan” is currently off the table, these results could lead to other exciting discoveries in the coming years.

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59 New Planets Discovered in Our Neighborhood

An artist’s concept of a high-resolution image of an Earth-size planet in the cool range of the habitable zone of a nearby M dwarf. © José A. Caballero (CAB, CSIC-INTA), Javier Bollaín (Render Area)

The hunt for habitable extrasolar planets continues! Thanks to dedicated missions like Kepler, TESS, and Hubble, the number of confirmed extrasolar planets has exploded in the past fifteen years (with 5,272 confirmed and counting!). At the same time, next-generation telescopes, spectrometers, and advanced imaging techniques are allowing astronomers to study exoplanet atmospheres more closely. In short, the field is shifting from the process of discovery to characterization, allowing astronomers to more tightly constraint habitability.

Finding potentially-habitable “Earth-like” planets around these fainter stars is the purpose of the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs (CARMENES), located at the Calar Alto Observatory in Spain. In a study that appeared in Astronomy & Astrophysics today, the CARMENES Consortium published data (Data Release 1) data from about 20,000 observations taken between 2016 and 2020. Among the measurements obtained from 362 nearby cool stars, the DR1 contained data on 59 new planets.

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Earth-Sized Planet Found At One of the Lightest Red Dwarfs

Artist’s conception of a rocky Earth-mass exoplanet like Wolf 1069 b orbiting a red dwarf star. If the planet has retained its atmosphere, chances are high that it would feature liquid water and habitable conditions over a wide area of its dayside. Image Credit: NASA/Ames Research Center/Daniel Rutter

Astronomers have found another Earth-sized planet. It’s about 31 light-years away and orbits in the habitable zone of a red dwarf star. It’s probably tidally locked, which can be a problem around red dwarf stars. But the team that found it is optimistic about its potential habitability.

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An Exoplanet is Definitely Orbiting Two Stars

Artist's impression of Kepler-16b, the first planet known to definitively orbit two stars - what's called a circumbinary planet. The planet, which can be seen in the foreground, was discovered by NASA's Kepler mission. Credit: NASA/JPL-Caltech/T. Pyle

Remember that iconic scene in Star Wars, where a young Skywalker steps out onto the surface of Tatooine and watches the setting of two suns? As it turns out, this may be what it is like for lifeforms on the exoplanet known as Kepler-16, a rocky planet that orbits in a binary star system. Originally discovered by NASA’s Kepler mission, an international team of astronomers recently confirmed that this planet orbits two stars at once – what is known as a circumbinary planet.

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A THIRD Planet Found Orbiting Nearby Proxima Centauri

This artist’s impression shows Proxima d, a planet candidate recently found orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The planet is believed to be rocky and to have a mass about a quarter that of Earth. Two other planets known to orbit Proxima Centauri are visible in the image too: Proxima b, a planet with about the same mass as Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

In August of 2016, astronomers with the European Southern Observatory (ESO) announced that they had discovered an exoplanet orbiting in neighboring Proxima Centauri. Based on Radial Velocity measurements (aka. Doppler Photometry), the discovery team estimated that the planet was roughly the same size and mass as Earth and orbited with Proxima Centauri’s Circumsolar Habitable Zone (HZ). In 2020, this planet was confirmed by follow-up observations.

In that same year, a second exoplanet (Proxima c) roughly seven times the mass of Earth (a Super-Earth or mini-Neptune) was confirmed. As if that wasn’t enough, an international team of astronomers with the ESO recently announced that they detected a third exoplanet around Proxima Centauri – Proxima d! This Mars-sized planet orbits about halfway between its host star and Proxima b and is one of the lightest exoplanets ever discovered.

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Two Earth-Like Worlds Found Orbiting a Red Dwarf Only 12.5 Light-Years Away

Artistic recreation of the Teegarden Star system. Credit: University of Göttingen

In the past few decades, there has been an explosion in the number of planets discovered beyond our Solar System. With over 4,000 confirmed exoplanets to date, the process has gradually shifted from discovery towards characterization. This consists of using refined techniques to determine just how likely a planet is to be habitable.

At the same time, astronomers continue to make discoveries regularly, some of which are right in our cosmic backyard. For instance, an international team of researchers recently detected two new Earth-like planets orbiting Teegarden’s Star, an M-type (red dwarf) star located just 12.5 light-years from the Solar System in the direction of the Aries constellation.

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What is the Direct Imaging Method?

Direct image of exoplanets around the star HR8799 using a Vortex coronagraph on a 1.5m portion of the Hale telescope. Credit: NASA/JPL-Caltech/Palomar Observatory

Welcome back to the latest installment in our series on Exoplanet-hunting methods. Today we begin with the very difficult, but very promising method known as Direct Imaging.

In the past few decades, the number of planets discovered beyond our Solar System has grown by leaps and bounds. As of October 4th, 2018, a total of 3,869 exoplanets have been confirmed in 2,887 planetary systems, with 638 systems hosting multiple planets. Unfortunately, due to the limitations astronomers have been forced to contend with, the vast majority of these have been detected using indirect methods.

So far, only a handful of planets have been discovered by being imaged as they orbited their stars (aka. Direct Imaging). While challenging compared to indirect methods, this method is the most promising when it comes to characterizing the atmospheres of exoplanets. So far, 100 planets have been confirmed in 82 planetary systems using this method, and many more are expected to be found in the near future.

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What is the Radial Velocity Method?

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser

Welcome back to our series on Exoplanet-Hunting methods! Today, we look at another widely-used and popular method of exoplanet detection, known as the Radial Velocity (aka. Doppler Spectroscopy) Method.

The hunt for extra-solar planets sure has heated up in the past decade or so! Thanks to improvements made in instrumentation and methodology, the number of exoplanets discovered (as of December 1st, 2017) has reached 3,710 planets in 2,780 star systems, with 621 system boasting multiple planets. Unfortunately, due to the limits astronomers are forced to contend with, the vast majority have been discovered using indirect methods.

When it comes to these indirect methods, one of the most popular and effective is the Radial Velocity Method – also known as Doppler Spectroscopy. This method relies on observing the spectra stars for signs of “wobble”, where the star is found to be moving towards and away from Earth. This movement is caused by the presence of planets, which exert a gravitational influence on their respective sun.

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Super-Earth Planet Found in the Habitable Zone of a Nearby Star

Artistic design of the super-Earth GJ 625 b and its star, GJ625 (Gliese 625). Credit: Gabriel Pérez/SMM (IAC)

M-type stars, also known as “red dwarfs”, have become a popular target for exoplanet hunters of late. This is understandable given the sheer number of terrestrial (i.e. rocky) planets that have been discovered orbiting around red dwarf stars in recent years. These discoveries include the closest exoplanet to our Solar System (Proxima b) and the seven planets discovered around TRAPPIST-1, three of which orbit within the star’s habitable zone.

The latest find comes from a team of international astronomers who discovered a planet around GJ 625, a red dwarf star located just 21 light years away from Earth. This terrestrial planet is roughly 2.82 times the mass of Earth (aka. a “super-Earth”) and orbits within the star’s habitable zone. Once again, news of this discovery is prompting questions about whether or not this world could indeed be habitable (and also inhabited).

The international team was led by Alejandro Mascareño of the Canary Islands Institute of Astrophysics (IAC), and includes members from the University of La Laguna and the University of Geneva. Their research was also supported by the Spanish National Research Council (CSIS), the Institute of Space Studies of Catalonia (IEEC), and the National Institute For Astrophysics (INAF).

Diagram showing GJ 625’s habitable zone in comparison’s to the Sun’s. Credit: IAC

The study which details their findings was recently accepted for publication by the journal Astronomy & Astrophysics, and appears online under the title “A super-Earth on the Inner Edge of the Habitable Zone of the Nearby M-dwarf GJ 625“. According to the study, the team used radial-velocity measurements of GJ 625 in order to determine the presence of a planet that has between two and three times the mass of Earth.

This discovery was part of the HArps-n red Dwarf Exoplanet Survey (HADES), which studies red dwarf stars to determine the presence of potentially habitable planets orbiting them. This survey relies on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) instrument – which is part of the 3.6-meter Galileo National Telescope (TNG) at the IAC’s Roque de Los Muchachos Observatory on the island of La Palma.

Using this instrument, the team collected high-resolution spectroscopic data of the GJ 625 system over the course of three years. Specifically, they measured small variations in the stars radial velocity, which are attributed to the gravitational pull of a planet. From a total of 151 spectra obtained, they were able to determine that the planet (GJ 625 b) was likely terrestrial and had a minimum mass of 2.82 ± 0.51 Earth masses.

Moreover, they obtained distance estimates that placed it roughly 0.078 AU from its star, and an orbital period estimate of 14.628 ± 0.013 days. At this distance, the planet’s orbit places it just within GJ 625’s habitable zone. Of course, this does not mean conclusively that the planet has conditions conducive to life on its surface, but it is an encouraging indication.

Tjhe Observatorio del Roque de los Muchachos, located on the island of La Palma. Credit: IAC

As Alejandro Suárez Mascareño explained in an IAC press release:

“As GJ 625 is a relatively cool star the planet is situated at the edge of its habitability zone, in which liquid water can exist on its surface. In fact, depending on the cloud cover of its atmosphere and on its rotation, it could potentially be habitable”.

This is not the first time that the HADES project detected an exoplanet around a red dwarf star. In fact, back in 2016, a team of international researchers used this project to discover 2 super-Earths orbiting GJ 3998, a red dwarf located about 58 ± 2.28 light years from Earth. Beyond HADES, this discovery is yet another in a long line of rocky exoplanets that have been discovered in the habitable zone of a nearby red dwarf star.

Such findings are very encouraging since red dwarfs are the most common type of star in the known Universe- accounting for an estimated 70% of stars in our galaxy alone. Combined with the fact that they can exist for up to 10 trillion years, red dwarf systems are considered a prime candidate in the search for habitable exoplanets.

But as with all other planets discovered around red dwarf stars, there are unresolved questions about how the star’s variability and stability could affect the planet. For starters, red dwarf stars are known to vary in brightness and periodically release gigantic flares. In addition, any planet close enough to be within the star’s habitable zone would likely be tidally-locked with it, meaning that one side would be exposed to a considerable amount of radiation.

Artist’s impression of of the exoplanets orbiting a red dwarf star. Credit: ESO/M. Kornmesser/N. Risinger (

As such, additional observations will need to be made of this exoplanet candidate using the time-tested transit method. According to Jonay Hernández – a professor from the University of La Laguna, a researcher with the IAC and one of the co-authors on the study – future studies using this method will not only be able to confirm the planet’s existence and characterize it, but also determine if there are any other planets in the system.

“In the future, new observing campaigns of photometric observations will be essential to try to detect the transit of this planet across its star, given its proximity to the Sun,” he said. “There is a possibility that there are more rocky planets around GJ 625 in orbits which are nearer to, or further away from the star, and within the habitability zone, which we will keep on combing”.

According to Rafael Rebolo – one of the study’s co-authors from the Univeristy of La Laguna, a research with the IAC, and a member of the CSIS – future surveys using the transit method will also allow astronomers to determine with a fair degree of certainty whether or not GJ 625 b has the all-important ingredient for habitability – i.e. an atmosphere:

“The detection of a transit will allow us to determine its radius and its density, and will allow us to characterize its atmosphere by the transmitted light observe using high resolution high stability spectrographs on the GTC or on telescopes of the next generation in the northern hemisphere, such as the Thirty Meter Telescope (TMT)”.

Artist’s impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL

But what is perhaps most exciting about this latest find is how it adds to the population of extra-solar planets within our cosmic neighborhood. Given their proximity, each of these planets represent a major opportunity for research. And as Dr. Mascareño told Universe Today via email:

“While we have already found more than 3600 extra-solar planets, the exoplanet population in our near neighborhood is still somewhat unknown. At 21 ly from the Sun, GJ 625 is one of the 100 nearest  stars, and right now GJ 625 b is one of the 30 nearest exoplanets detected and the 6th nearest potentially habitable exoplanet.”

Once again, ongoing surveys of nearby star systems is providing plenty of potential targets in the search for life beyond our Solar System. And with both ground-based and space-based next-generation telescopes joining the search, we can expect to find many, many more candidates in the coming years. In the meantime, be sure to check out this animation of GJ 625 b and its parent star:

Further Reading: arXiv, IAC