A giant exoplanet has been discovered orbiting a tiny white dwarf star only a quarter of the planet’s size. That’s right, the planet is far larger in size than its star. Find out why this matters to our search for life on other worlds.
I can vividly remember turning on the television to catch the very first pictures ever taken on the surface of the planet Mars. We didn’t even know if there were planets beyond our solar system, the so-called exoplanets, in those early days. For all we knew, Mars might have been the only place we would ever be able to search for life.
It was in July 1976, and I was fifteen at the time. NASA had planned it to take place on the 4th of July, but it ended up being on the 20th, the same day as the Apollo 11 moon landing.
We were still in awe of our brand new RCA colour TV. Dad had splurged on it a couple of years earlier. We arranged all of our living room furniture with vantage points towards its screen. It was a quirky old house with a fireplace. Still, in the 70s, people gathered around the new electronic hearth instead of basking at traditional firesides.
PHOTOGRAPHS FROM VIKING 1 LANDER ARRIVE ON SCREEN
I remember waiting to see the first photographs from the Viking 1 lander arrive on the screen. One thing we had to get used to was the speed of light. It created a lengthy delay between when Viking 1 did anything and when we received its signal. That included the news of its landing. The photons from exoplanets can take centuries to reach us, but our imaginations hadn’t absorbed that idea yet.
As a result, for a tantalizing 15 minutes or so, Viking had landed, but its signal had to make it through space from Mars to Earth at light’s constant speed. Nobody knew for sure how the landing had turned out, including Mission Control. For most of us, it was our first practical encounter with the idea that light has a fixed velocity and isn’t everywhere instantly at the flip of a switch.
The images were panoramas taken by a rotating camera head. They started the moment the lander touched down. The very first images were black and white.
MARS LOOKED EERILY EARTHLIKE
Mars looked eerily earthlike. In those days, people had only ever seen the earth and the moon. Mars’ atmosphere made it look much more like home than the moon. For one thing, it had a daytime sky instead of the bleak day and night lunar blackness.
Off in the Martian background from the lander, there were low, weathered mountains, and in the foreground, we could see bits of the lander. In between was a sterile, barren, stony desert. It looked inhospitable but not alien.
In the colour shots that came out the next day, we could see that Mars genuinely was a very red planet. The ground and the sky were both reddish.
PLANNED FOR 90 DAYS – KEPT WORKING FOR 6 1/2 YEARS
NASA’s mission plan expected the lander to last for 90 days. Instead, Viking 1 kept working for 61/2 years. It only shut down because of a bug in a software update sent from mission control in 1982. Disappointingly, despite countless jokes about little green men hiding behind the camera as it rotated, Viking 1’s onboard mini-lab could find no evidence of life on Mars.
We have never found evidence of life on other worlds. There are some potential habitats elsewhere in our solar system. They’re not any of the planets; they’re moons. The two satellites at the top of the shortlist are Europa, which orbits Jupiter and Enceladus, which is one of Saturn’s countless moons.
At the same time, researchers now devote a great deal of energy to the exoplanets. People weren’t sure that planets outside our solar system existed until 1992.
ABOUT 4,000 CONFIRMED EXOPLANETS
That’s when astronomers Aleksander Wolszczan and Dale Frail detected two massive exoplanets orbiting a pulsar. We had to wait until 1995 before graduate student Didier Queloz spotted a world about the size of Jupiter orbiting a star like our sun. Today, scientists have detected just about 4,000 confirmed exoplanets and another 3,000 possible candidates.
That ongoing search turned up a bizarre phenomenon last week. When stars like the sun die, they swell up into a red giant roughly 100 times the mass of the sun. Then they lose about half of their weight and condense down to a volume only the size of the earth. Astronomers call stars at this end stage of life white dwarfs.
A research team from the University of Warwick’s Department of Physics and the Millennium Nucleus for Planet Formation (NPF) at the University of Valparaíso was reviewing a survey of ten thousand white dwarf stars in search of exoplanets. The stars came from the Sloan Digital Sky Survey.
STRANGE BURSTS OF HYDROGEN, OXYGEN AND SULPHUR
By analyzing nuanced shifts in the light from each star system, they could determine the chemical elements surrounding the star. They noticed tiny bursts of hydrogen in the data. That’s a bit strange, but even stranger was the presence of oxygen and sulphur.
The Very Large Telescope of the European Southern Observatory in Chile (VLT) has appeared in quite a few of our stories lately. It turns up here again. The VLT enabled the team to see that the hydrogen, oxygen and sulphur formed a ring of gas.
Dr. Boris Gaensicke, from the University of Warwick, is the lead author of the study published last week in the journal Nature. He said this about the team’s discovery, “At first, we thought that this was a binary star with an accretion disc formed from mass flowing between the two stars. However, our observations show that it is a single white dwarf with a disc around it roughly ten times the size of our sun, made solely of hydrogen, oxygen and sulphur. Such a system has never been seen before, and it was immediately clear to me that this was a unique star.”
A YEAR THERE ONLY LASTS TEN DAYS
The exoplanet they have discovered orbiting this “unique star” is a gas giant like Neptune. Except, instead of orbiting off in the outskirts 4.5 billion kilometres from the sun, this planet is so close to its star that a year there only lasts ten days.
For perspective, a year on Mercury is 88 days long. Even more bizarre, this newly discovered world is four times larger than its sun. You read that correctly. The giant exoplanet is much larger in size than the star it orbits.
The gases that the team detected come from the exoplanet’s atmosphere. The white dwarf star is stripping it away. The loss is not because of gravity but because of heat. Dr. Gensicke explains, “This star has a planet that we can’t see directly, but because the star is so hot it is evaporating the planet, and we detect the atmosphere it is losing.”
STAR SO HOT IT IS EVAPORATING THE PLANET
Dr. Matthias Schreiber from the University of Valparaiso, added, “We were stunned when we realized that when observing hot white dwarfs, we are potentially seeing signatures from extrasolar planet atmospheres. While this hypothesis needs further confirmation, it might indeed open the doors towards understanding extrasolar planet atmospheres.”
Assuming that our planet is typical, if we want to find life, we need to find atmospheres. Understanding how atmospheres work on exoplanets is an essential step in that direction. This discovery moves us closer to being able to tell the story of our place in the universe.
We always have more to learn if we dare to know.
University of Warwick
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