Big planet orbiting star challenges what we know about space

Astronomers have been left baffled by a strange discovery in space that goes against current theories around how planets are formed.

Researchers from the University of Warwick and University College London’s Mullard Space Science Laboratory in England have found a really big planet orbiting a very small star.

With a mass only one fifth that of the sun, the star was discovered to have a massive gas planet TOI-6894b circling around it.

While it’s not unusual for a planet to orbit a star, like our sun, this particular star, called Star TOI-6894, is currently the smallest known star to host an orbiting giant planet.

In fact, the star is a red dwarf*, one of the most commonly found stars in the Milky Way*.

Current theories on the way planets are formed state that stars this size would only be able to host small planets. However, TOI-6894b is much larger. The study suggests the exoplanet* is as big as Saturn, which is the second-biggest planet in our solar system, though it only has about half its mass.

One of the researchers involved in the study, University of Warwick Associate Professor Dr Daniel Bayliss said the discovery means there could be more giant planets out there than originally thought.

“Most stars in our galaxy are actually small stars exactly like this, with low masses and previously thought to not be able to host gas giant planets,” Dr Bayliss said. “So, the fact that this star hosts a giant planet has big implications* for the total number of giant planets we estimate exist in our galaxy.”

The planet was discovered by analysing TESS (Transiting* Exoplanet Survey Satellite) data in order to search for signs of giant planets around low-mass stars.

Lead author of the study Dr Edward Bryant said he was very excited by the discovery after searching through TESS data on 91,000 low-mass red-dwarf stars.

“Then, using observations taken with one of the world’s largest telescopes, ESO’s VLT, I discovered TOI-6894b,” he said. “We did not expect planets like TOI-6894b to be able to form around stars this low-mass. This discovery will be a cornerstone* for understanding the extremes of giant planet formation.”

HOW DO PLANETS FORM?
Scientists have long accepted a theory on planet formation called the core accretion theory. This theory holds that a planetary core* forms first through a process called accretion. Accretion is the gradual build up of materials. You could imagine it like a snowball rolling down a hill, picking up more and more snow – except it’s a ball of gas, collecting more gas from around it.

As the core gets bigger and bigger it attracts more gases. These gases then form an atmosphere*. It then gets massive enough to enter a runaway gas accretion process to become a gas giant, which is where it picks up gases at extreme speed, supercharging its growth into a planet.

But for this theory to work, a giant gas planet needs to be able to suck in a certain amount of gas and dust from the protoplanetary disc* around the star, in order to form the planet’s core and start the runaway process. It’s the runaway process which transforms the growing ball of gas into a planet. Low-mass stars don’t have enough of this raw material to form a massive enough core and start the accretion process.

Now, the discovery of giant gas planet TOI-6894b orbiting an extremely low-mass star has thrown this whole theory into question.

Dr Vincent Van Eylen, from UCL’s Mullard Space Science Laboratory, said: “It’s an intriguing discovery. We don’t really understand how a star with so little mass can form such a massive planet. This is one of the goals of the search for more exoplanets. By finding planetary systems different from our solar system, we can test our models and better understand how our own solar system formed.”

POLL

GLOSSARY

• red dwarf: the smallest kind of hydrogen burning star and the most numerous star in the galaxy
• Milky Way: a spiral galaxy with billions of stars in it as well as our solar system
• implications: conclusions that can be drawn from the research
• transiting: moving, travelling
• exoplanet: a planet that is orbiting a star outside our solar system
• cornerstone: something on which a theory is based
• core: the innermost part of a planet
• atmosphere: a layer of gas surrounding a planet
• protoplanetary disc: a spinning disk of gas and dust that orbits a newly formed star

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QUICK QUIZ
1. What is the name of the star that was discovered to have a gas giant orbiting around it?
2. What type of star is it?
3. What is its mass in relation to the sun?
4. Why is this discovery so significant?
5. How was it discovered?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Storyboard
Convert the information provided about the core accretion theory into an illustrated storyboard to show how gas giants were believed to be formed prior to the discovery of TOI-6894b.

Time: allow 20 minutes to complete this activity
Curriculum Links: English; Science

2. Extension
Write at least five interview questions that you could ask the scientists involved in this discovery. Word your questions so that they show understanding of the information already presented while probing for further answers or possibilities.

Time: allow 20 minutes to complete this activity
Curriculum Links: English; Science

VCOP ACTIVITY
Read this!
A headline on an article – or a title on your text – should capture the attention of the audience, telling them to read this now. So choosing the perfect words for a headline or title is very important.

Create three new headlines for the events that took place in this article. Remember, what you write and how you write it will set the pace for the whole text, so make sure it matches.

Read out your headlines to a partner and discuss what the article will be about based on the headline you created. Discuss the tone and mood you set in just your few, short words. Does it do the article justice? Will it capture the audience’s attention the way you hoped? Would you want to read more?

Consider how a headline or title is similar to using short, sharp sentences throughout your text. They can be just as important as complex ones. Go through the last text you wrote and highlight any short, sharp sentences that capture the audience.