Tag Archives: Proxima centauri

New planet found “next door” to our solar system

At one quarter the mass of the Earth, the newly-discovered planet is not only one of the closest planets we know of, but also one of the lightest. The planet is named Proxima d.

Artist’s impression of the newly-discovered planet. Image credits: Credit: ESO/L. Calçada.

Hey planet, here’s an ESPRESSO

In 1915, the Scottish astronomer Robert Innes discovered a new star. He called it Proxima Centauri (or rather, Proxima Centaurus).

Proxima Centauri is the closest star to Earth, lying just over four light-years away — and will continue to be so for about 25,000 years, after which Alpha Centauri A and Alpha Centauri B will move closer to our solar system and will take alternating turns as the “closest star to Earth” (for about 80 years each).

But it took another hundred years after the star was named for the first planet in the Proxima Centauri solar system to be discovered. Astronomers are nothing if not methodical, so in 2016, when they discovered a planet, they called it Proxima b. They found another planet candidate in 2019 which they called Proxima c. Now, they’ve discovered a new planet and named it (you’ve guessed it) Proxima d.

“The discovery shows that our closest stellar neighbor seems to be packed with interesting new worlds, within reach of further study and future exploration,” explains João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal and lead author of the study published today in Astronomy & Astrophysics.

The planet was first discovered in 2020, and was now confirmed with the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO).

“After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth.”  

The planet was discovered using a less common method. Because planets don’t emit their own light, researchers rely on indirect information to find them. Most commonly, they use a method called the transit method — basically, they measure the luminosity coming from a star and look for dips in luminosity caused by planets passing in front of that star. But Proxima d was discovered using the radial velocity technique.

The technique works by detecting tiny wobbles in the motion of the star — wobbles created by a planet’s gravitational pull. With this, they can not only detect the presence of a star but also calculate its mass.

A depiction of the radial velocity method showing how a smaller object (such as an extrasolar planet) orbiting a larger object (such as a star) could produce changes in position and velocity of the latter as they orbit their common center of mass (red cross). Image via Wiki Commons.

“This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”

“This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds.

The gravitational effect of Proxima d is pretty small — it only causes Proxima Centauri to wobble by around 40 centimeters per second (1.44 km/hour) — and it’s striking that astronomers can detect these small differences from 4 light-years away. Based on this, researchers calculated that the planet is around one-quarter the mass of the Earth and one of the lightest exoplanets ever found.

This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The picture was created from pictures forming part of the Digitized Sky Survey 2. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in color like the Sun. Image credits: Digitized Sky Survey 2. Acknowledgment: Davide De Martin/Mahdi Zamani.

The planet does not lie in the habitable zone. Although the star is a red dwarf star with a mass around 8 times lower than that of the Sun, the planet simply orbits the star too closely. Assuming an Earth-like reflectivity of the planet, the surface temperature would be 87 °C (188 °F) — too hot to support life as we know it. Another Proxima Centauri planet (Proxima b) could lie in the habitable zone, but this is still disputed by astronomers.

Researchers expect more intriguing data to come from ESPRESSO’s search for other worlds, especially as it will soon be complemented by ESO’s Extremely Large Telescope (ELT), currently under construction in the Atacama Desert. Together, these two will enable researchers to discover and study many more planets around nearby stars.

The study was published in the journal Astronomy and Astrophysics.

Proxima Flaresauri.

Massive flare in the Proxima Centauri system puts its habitability into question

The Sun’s closest neighboring star, Proxima Centauri, might not be as welcoming as we believed — a team of astronomers have detected a flare so powerful from the star that it throws the habitability of its system into serious doubt.

Proxima Flaresauri.

Artist’s impression of a flare from Proxima Centauri.
Image credits Roberto Molar Candanosa / Carnegie Institution for, NASA/SDO, NASA/JPL.

A team of astronomers led by Meredith MacGregor from the Carnegie Institution for Science discovered the flare while reanalyzing recordings taken last year by the Atacama Large Millimeter/submillimeter Array (ALMA), an array of 66 radiotelescope antennas nestled in the Atacama desert.

Now, by their very nature, solar flares are some of the most violent and energetic events we know of. Think of them as magnetic short-circuits in a star. What happens during a flare is that ebbs and flows in a star’s magnetic field start accelerating electrons (negatively-charged particles) close to the speed of light. Enough of these build up that they start interacting with stellar plasma (highly electrically charged atoms), ripping it out of the star, causing it to erupt. This eruption can be seen across the electromagnetic spectrum.

And that’s where the bad news starts: even by solar flare standards, what the team discovered was humblingly violent. The flare they detected from Proxima Centauri was over 10 times brighter, at its peak, than the largest flares that we’ve ever recorded from the Sun at similar wavelengths.

“March 24, 2017 was no ordinary day for Proxima Cen,” said MacGregor.

The flare increased Proxima Centauri’s brightness by a factor of 1,000 over 10 seconds. It was also preceded by a smaller flare. Taken together, the event lasted for under two minutes — which would explain why nobody noticed them in the first place. For context, ALMA observed the star for over 10 hours between January and March of last year, when the flares erupted.

We knew from previous observation that Proxima Centauri was prone to regular bouts of flares, although they were much smaller and emitted chiefly in the x-ray spectrum. However, the findings now cast a lot of doubt on the habitability of the exoplanet Proxima b, which up to now raised a lot of interest as a potentially habitable planet. Proxima b orbits its star around 20 times closer than the Earth orbits the Sun, so flares of this magnitude are a huge problem. The team estimates that a flare 10 times larger than a major solar flare would drench the planet with 4,000 times more radiation that Earth gets from a solar flare. That’s enough to raise literal hell on the planet, the team explains:

“It’s likely that Proxima b was blasted by high energy radiation during this flare,” says MacGregor.

“Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”

So it might be healthier to steer away from Proxima b until we find a way to accurately predict, and then successfully weather, these flares.

The findings also allowed the team to get a better image of the Proxima Centauri system, and infirm previous estimation that it contains large bodies of dust and larger particles, similar to our asteroid belt.

The paper “Detection of a Millimeter Flare From Proxima Centauri” has been published in the journal Astrophysical Journal Letters.

Proxima Centauri is more like Earth than we thought, might host habitable planet

Proxima Centauri, the closest star to our solar system, may have a lot in common with the Sun – but we don’t know if this is good news or bad news.

A group of sunspots. The big one in the lower-left part of the image stretches more than 11 Earths, or 87,000 miles across. Image by NASA.

With the sheer multitude of stars and planets in the Milky Way galaxy, you wouldn’t expect to find habitable planets right next door – but this might be the case. In August, astronomers announced that the nearby star Proxima Centauri hosts an Earth-sized planet (called Proxima b) in its habitable zone. We got a bit excited then, but our excitement was short lived. Proxima Centauri is nothing like our Sun.

Proxima is a small, dim, red dwarf, about 1,000 times less luminous than the Sun. That hasn’t changed one bit, but the two stars do share a striking similarity: a sunspot cycle.

You missed a spot

Sunspots are darker spots of reduced temperature which are caused by concentrations of magnetic field flux that inhibit convection. They usually appear in pairs, of opposite magnetic polarity. Our Sun has an 11-year sunspot cycle: at the start of the cycle there almost no spots, and towards the end, an average 100 sunspots cover the star’s surface.

Proxima has a similar 7-year cycle, except it’s much more dramatic. At its peak, almost 20% of the star is covered by spots.

“If intelligent aliens were living on Proxima b, they would have a very dramatic view,” says lead author Brad Wargelin of the Harvard-Smithsonian Center for Astrophysics (CfA).

It was quite surprising to make this discovery because aside from the differences in size, the interior of the two stars is expected to be different.

Convection here, convection there

The different transport mechanisms of low-mass, intermediate-mass, and high-mass stars. Image from Sun, via Wikipedia.

Inside the Sun, there is a lot of convection going on – but only on the outer areas. There is a lot of matter circulation in the outer third of the Sun (think water inside a boiling pot) but the inner parts are quite still. There’s actually a difference of rotation between two parts, which many astronomers believe is causing the Sun’s magnetic activity.

In contrast, you’d expect convection to happen all through Proxima Centauri so there wouldn’t be any difference in rotation, any magnetic contrast and therefore, any spots.

Sadly, this poses more questions than it answers.

“The existence of a cycle in Proxima Centauri shows that we don’t understand how stars’ magnetic fields are generated as well as we thought we did,” says Smithsonian co-author Jeremy Drake.

Unfortunately, these questions won’t be answered anytime soon.

“Direct observations of Proxima b won’t happen for a long time. Until then, our best bet is to study the star and then plug that information into theories about star-planet interactions,” says co-author Steve Saar.

To make it even worse, we’re not sure how this would affect habitability around Proxima Centauri. There’s a good chance it could have a negative impact because the sunspot cycle could drive solar winds to burn up huge chunks of the planet’s atmosphere (assuming there is an atmosphere in the first place). This would imply that Proxima b is much like the Earth’s moon: in the right place for life to exist, but completely barren and without an atmosphere.