How can a blurry image of a star help us understand more about their orbiting exoplanets than
a clear, sharp image?
It may seem counterintuitive, but that’s exactly what CHEOPS, or the CHaracterising
ExOPlanets Satellite, is doing!
CHEOPS is a space telescope launched by the European Space Agency in December of last
year, with a mission to hunt down the most earth-like exoplanets, which, as you can probably
imagine considering the distances involved, is not an easy feat.
I’m Alex McColgan and you are watching Astrum, and in this video we will talk about the very
promising ESA mission, CHEOPS.
This video is a collaboration with our Spanish channel, Astrum Español, which you can find
a link to here and in the description.
Please show Rafa, our Spanish host, some support, I think he’s doing a great job and if you
are a Spanish speaker make sure to take a look at his channel.
CHEOPS is a joint effort with ESA and the Swiss Space Office, which is fitting as it
was swiss astronomers who discovered the first exoplanet back in 1995.
It’s hard to believe given that we now have confirmed the existence of thousands of exoplanets,
but it was only 25 years ago when we discovered the first one, so we’re still in the early
days of this astronomical field.
The planet they discovered is now called 51 Pegasi-b, or Dimidium, a gas giant around
50 light-years away in the constellation Pegasus.
It is now considered the prototype for what has come to be known as Hot Jupiters.
These planets are similar in size to our gas giant neighbour, but orbit their parent star
very tightly, some with orbital periods of 10 or less days.
This means they are extremely hot due to their close proximity to their sun.
The reason exoplanets are only just being discovered is because they are exceptionally
difficult to observe, as they are hidden by the brightness of their stars.
That’s why we have to really think outside the box if we want to detect them.
If you use a regular telescope to look at stars that are known to have exoplanets orbiting
them, you’ll see only the shine of the star, as its brightness compared to any close orbiting
exoplanet is overwhelming.
You can’t even directly see exoplanets around the closest star system to us, Alpha Centauri,
which is only 4 light years away from us.
If that is our closest neighbour, and directly observing through a regular telescope doesn’t
work, imagine trying to observe exoplanets 10s to 100s of light years away.
So, how did those astronomers discover Dimidium?
Hot Jupiters are often the easiest types to discover, if something like that can really
be considered easy.
Because they have a strong gravity and are close enough to their parent star, they both
orbit each other around a centre of mass that makes the star appear like it’s wobbling.
Depending on the mass of the bodies, the centre of mass can be within the parent object, or
with objects of a similar mass, it could simply be a point in space.
Wherever the centre of mass is located is known as the barycentre.
One of the most extreme examples in our solar system is Pluto and Charon, which orbit around
a point above Pluto’s surface.
In regards to Dimidium, astronomers could detect shifts in the distant star’s light,
and confirm the presence of a large exoplanet because it’s causing the star to wobble.
This method of detection is called the Radial Velocity Method, or Doppler Spectroscopy.
The discovery of Dimidium, made by the ELODIE spectrograph in France, won the astronomers
a Nobel Prize, as it was considered a major breakthrough for European astronomy.
Since then, there have been many new exoplanet discoveries and we know now that our galaxy
is teeming with planets.
This is where the CHEOPS mission comes in.
It is already in orbit and sending back more than 1GB data every day.
CHEOPS orbits in what is called an heliosynchronous orbit, 700km up around Earth.
In other words, CHEOPS is in a dawn/dusk polar orbit.
That means that it travels around Earth along the twilight terminator line, with the Sun
powering up its solar panels on its back.
Meanwhile, its gaze peers deep into space, protected from sunlight interference.
CHEOPS’ instruments allow the telescope to study the smallest exoplanets we know,
called super-earths.
They can be as small as our planet but can also be as big as Neptune.
The goal of CHEOPS is not to find new exoplanets but to examine ones we already know about
to determine what they are made of and how they formed.
And that is very exciting because it has the capabilities of discovering potentially habitable
worlds.
Planets that might have a similar size, orbit and composition to our home.
CHEOPS is much smaller than Hubble, it’s only a 1.5m across and uses a 32cm mirror,
however it can see exactly what the designers had hoped for.
And here is its first glance at the stars.
Now, something about this image is very peculiar, all the stars imaged here are blurry and no
exoplanets are visible!
No, this isn’t a design flaw, CHEOPS is working as intended.
The reason for the blurry image has something to do with the second method of exoplanet
discovery, namely, transit photometry.
One of CHEOPS key instruments is a very advanced photometer, that can detect the tiniest amount
of light variations on distant stars.
If an exoplanet’s orbit is aligned with us, it will transit the parent star so that
it covers some of the star’s disk from our perspective, in a similar fashion to a tiny
eclipse.
And that’s what CHEOPS does, it monitors the amount of light it receives from a specific
star, and then detects light variations from when a planet crosses in front of its disk,
to see how much dimmer it gets.
The reason the CHEOPS image is blurry is so that light from the star hits more of the
camera sensor, increasing the number of pixels that get hit by the star’s light.
Through this, astronomers don’t need to see the exoplanet itself, but this increased
resolution allows astronomers to accurately record and study the star’s light spectra
itself as well as any changes that take place from the exoplanet’s transit.
As you can guess, the bigger the planet, the more light it will obscure and the easier
it will be to notice a dip in light intensity.
For small planets, however, this process is much more difficult to measure.
And that’s why CHEOPS is so important, as its advanced instruments and blurry images
allow astronomers to better define the transits of those smaller, more earth-like planets.
Additionally, CHEOPS can measure a planet’s Phase Curve, or how much light it reflects
from its Sun.
When a planet is in front of the star it will block light, but as it orbits around to the
sides it will reflect light back to us which makes the star appear a little brighter from
our perspective.
Here, CHEOPS’ photometer comes in handy again, this time to measure the increment
in light variation.
By comparing it to the light we receive when the planet is behind the star, when it’s
not interfering with the star’s brightness, scientists should be able to isolate the spectrum
of light reflected by the planet.
With that, they will be able to know the composition of the planet’s atmosphere.
And since they are investigating only the most promising planets, they can take multiple
readings for a more defined measurement.
Why does CHEOPS have to be in space?
Can’t we do all these readings from Earth?
Well, just like with the James Webb telescope, telescopes here on Earth face two main hurdles.
The first one is that we have night and day.
That’s a large section of a 24-hour period where no observations can take place.
We might miss an important transit during that time.
But even at night, the light a telescope receives is distorted as it travels through Earth’s
atmosphere.
Photons hit several particles in the different layers of the air, making the light flicker
and wobble.
Even if there are several methods to counter that, the readings would never be as accurate
as they would be in space.
That’s why CHEOPS was launched into a sun-synchronous orbit.
As I mentioned before, it will ride the terminator line of Earth.
This not only allows it to receive constant light on its back for the solar panels to
generate power, but also means it can take a look at the stars 24/7, without sunlight
interfering with its readings.
So, as you can see, with all the data CHEOPS will hopefully collect, it may just be a matter
of time until we confirm the existence of another planet like Earth.
A planet with similar mass and temperature, with the presence of water and oxygen in its
atmosphere: All the right conditions that harboured life here.
I will definitely keep an eye on CHEOPS, and I hope to make a video about its fascinating
discoveries in the future!
Thanks for watching, and thanks as well to Rafa for helping with this video.
Make sure to show him some love over on the Astrum Spanish channel, which you can find
here and in the description.
A big thanks as well to my Patrons and Members that support the channel, your help really
goes a long way and allows me to make videos like these in the future.
If you want to support too, find the links in the description.
All the best and see you next time!