Candidate exoplanet spotted in the habitable zone of Alpha Centauri system!
Would you observe a star for a hundred hours in order to find a new habitable planet?
To me, it seems... pretty fair. Looking directly at planets that could
support life around nearby stars: this is what a new technique proposed by a team of astronomers
and presented in Nature Communications can do. The study, which aimed to find a potentially habitable
planet within the Alpha Centauri system, after nearly 100 hours of observation and 7 terabytes
of images taken, revealed a signal - the candidate planet C1. The technique is promising and
revolutionary, but further verification is needed before the nature of the issue can be confirmed.
Follow me on this video if you're hoping that - somewhere out there - there is life as we know it!
A primary pursuit of modern astronomy is the search for worlds that are potentially
similar to Earth. Such worlds would help us to understand the context of our own planet
and would themselves become targets of searches for life beyond the solar system.
Meanwhile, giant exoplanets have been imaged on wide orbits—enabling direct studies of
their orbits and atmosphere. To enable finding and exploring potentially Earth-like planets,
exoplanet imaging capabilities are progressing towards lower-mass planets
in the habitable zones of nearby stars. In this context, habitable refers to the possibility of
a planet with a broadly Earth-like atmosphere to host liquid water on its surface. The
nearest stellar system, α Centauri, is among the best-suited for imaging habitable-zone exoplanets.
The primary components α Centauri A and B are similar in mass and temperature to the Sun,
and their habitable zones are at separations of about one AU. At the system’s distance of 1.3 pc,
these physical separations correspond to angular separations of about one arcsecond, which can
be resolved with existing 8-m-class telescopes. However, no planets are currently known to orbit
either star. Measurements of the stars’ radial velocity (RV) trends exclude planets more massive
than M≥ 53 Earth-masses (M⊕) in the habitable zone of α Centauri A, and ≥ 8.4 M⊕ for α Centauri B.
But let's go deeper into it: how do we search for an exoplanet?
Looking for exoplanets, in the practice of research, almost never really translates
into looking for exoplanets. Rather, we observe the stars that seem optimal candidates to host
planetary systems, we study their light and break it down to look for traces of
the presence of other worlds. For example, you look at whether their light varies in intensity
periodically due to the transit of a body that does not emit light in front - the
transits technique - or if the star is moving a little here and there.
disturbed by the gravitational influence of his court - the technique of radial velocities.
We hardly ever try to observe the planets directly! Too hard to see, especially Earth-like
ones: too small and dark for the star's blinding light. It is much easier to find gaseous planets,
much larger than Jupiter and orbiting young stars, far away from the habitable zone.
Nothing more inhospitable for life. That's why, if you take a look at known exoplanets,
you'll find out that we know a lot of Giant planets and very few of the small ones.
In reality, there are a lot of small planets, too! It's just that we can't detect them,
because of the limits of our technology. For this reason, the study of the planets in the
so-called habitable zones has so far been carried out mainly through the first two methods - or with
a combination of the two. And for the same reason the article published some days ago,
Wednesday 11 February, in Nature Communications, represents a real
novelty in the field. The authors of the study have in fact set up and tested a new method
for making direct images of exoplanets in the habitable zone of nearby stars.
This is a mid-infrared imaging technique which, if integrated for a very long observation time
(of the order of one hundred hours!), can directly capture images of planets about
three times the size of Earth within the habitable zones of nearby stars.
Let's make it clearer: It would be like being able to observe a tennis
ball from a distance of about 60.000 km! "If we want to find planets with conditions
suitable for life as we know it, we have to look for rocky planets roughly the size of Earth,
within habitable zones around older, Sun-like stars,"
explains Kevin Wagner, first author of 'article, postdoc researcher
with NASA's Hubble Fellowship program at the University of Arizona Steward Observatory.
The method described in Wagner and colleagues' paper for finding these objects can increase the
current ability to directly observe exoplanets more than tenfold. In addition to the technical
difficulties, in fact, another problem of the approach adopted so far concerned the observed
light frequencies: most of the attempts at direct imaging of exoplanets concentrated
at infrared wavelengths below 10 microns, just below the regime. where such planets shine more.
There is a good reason for this: the Earth itself is bright at these wavelengths.
The infrared emission of the sky, of the camera and of the telescope itself, however, greatly
dilute the signal. But the strong motivation for continuing to search at these wavelengths is that
that's where an Earth-like planet in the habitable zone around a Sun-like star will shine the most. '
The team used ESO's Very Large Telescope (Vlt) in Chile to observe our closest star system:
Alpha Centauri, just 4.4 light-years away. Alpha Centauri is a triple star system:
it is composed of two stars - Alpha Centauri A and B - similar to the Sun in size and age
and which orbit each other like a binary system and a third star - Alpha Centauri C,
but better known as Proxima Centauri -, a much smaller red dwarf that orbits
its two sisters at a great distance. A planet no more than twice the size
of the Earth-orbiting in the habitable zone around Proxima Centauri has already
been observed - indirectly - through the technique of radial velocities.
According to the study authors, Alpha Centauri A and B could also host similar planets, but
indirect detection methods are still not sensitive enough to find rocky planets in their habitable
zones - further away than their companion. To increase sensitivity when taking images,
the scientists used an adaptive secondary mirror in the telescope
to correct for the distortion of light caused by turbulence in the Earth's atmosphere. Besides, the
researchers used a coronograph - a kind of mask to cover the direct light coming from the stars,
used on one of them at a time -, and optimized it for mid-infrared wavelengths. Finally, to observe
the habitable zones of both stars simultaneously, the scientists moved rapidly and continuously
from Alpha Centauri A to Alpha Centauri B. “We were able to invert the star covered by
the coronograph every tenth of a second,” explains Wagner. "This allowed us to observe each star for
half the total time and, importantly, allowed us to subtract each frame from the next frame,
removing all that noise from the camera and telescope."
The speed of execution of this alternation of pointing is really fundamental at infrared
wavelengths - much more than in other domains of the electromagnetic spectrum - since the thermal
emission - of the sky but also objects - is very variable over time and it is important to always
subtract two frames with the closest possible noise. Thanks to this approach, scientists were
able to remove most of the unwanted noise by opening the door to the detection of much weaker
signals created by the planets they searched for. The observations of Alpha Centauri, as we said,
lasted for a total of almost one hundred hours over a month in 2019, and count more
than 5 million images. Imagine there is some form of life in the Alpha Centaury system,
let's say an intelligent form of life: if it knew that, it would think that we're literally invading
his own privacy! We are... universe-stalkers! Anyway...the 7 terabytes of data collected
have been made publicly available. (7 terabytes! Just to emphasize it better...)
This is one of the first direct imaging campaigns of exoplanets that used and “stacked” the data
collected over several nights of observation to increase the final sensitivity. After removing
the artefacts - false signals created by the instrumentation and residual light from the
coronagraph - the final image revealed a presence, which scientists have indicated as "C1": it could
be an exoplanet within the habitable zone. "There is a point source that looks like what
we would expect to see from a planet, and that we would not be able to attribute to any of the
systematic error corrections," says Wagner. The simulations suggest that "C1" could be a
planet with dimensions between Neptune and Saturn at a distance from Alpha Centauri A
similar to the distance between the Earth and the Sun. However, the authors clearly
state that the confidence level achieved by the data is not it allows affirming with certainty
the nature of the planet and that subsequent verifications will be necessary to exclude the
possibility that C1 is generated by some unknown artefact coming from the instrument itself.
What about future observations? "Before finding out the answer to this question,
be sure to like or dislike the video so that we can continue to improve
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It’s worth keeping in mind that the coming extremely large telescopes will bring significant
new capabilities to ground-based imaging of planets around nearby stars. Whether or not we
have a new planet in this nearest of all stellar systems to Earth, we do have significant progress
at pushing the limits of ground-based observation, with positive implications for the ELTs.
New, interesting candidates to look at are Sirius, the brightest star in the night sky,
and Tau Ceti, which hosts a planetary system that has already been observed indirectly.
Making this technique a routine observation mode - and therefore being able to take the
temperature of the planets that orbit within the habitable zones of nearby stars - will
be a turning point for the exploration of new worlds and the search for life in the universe.
"This video ends here! Thanks for watching everyone! Are you in love with exoplanets?
What's the weirdest one you know? Is there anything more you want to hear? Let us know
in the comments below, be sure to subscribe, and I'll see you next time on the channel!"