This text was initially revealed at The Conversation. The publication contributed the article to Area.com’s Professional Voices: Op-Ed & Insights.
The solar will sometime die. It will occur when it runs out of hydrogen gasoline in its core and might not produce vitality through nuclear fusion because it does now. The loss of life of the solar is commonly regarded as the top of the photo voltaic system. However in actuality, it might be the start of a brand new part of life for all of the objects dwelling within the photo voltaic system.
When stars just like the solar die, they undergo a part of fast enlargement referred to as the Red Giant phase: The radius of the star gets bigger, and its color gets redder. Once the gravity on the star’s surface is no longer strong enough for it to hold on to its outer layers, a large fraction – up to about half – of its mass escapes into space, leaving behind a remnant called a white dwarf.
I’m a professor of astronomy on the College of Wisconsin-Madison. In 2020, my colleagues and I discovered the first intact planet orbiting round a white dwarf. Since then, I have been fascinated by the prospect of life on planets round these, tiny, dense white dwarfs.
Researchers seek for indicators of life within the universe by ready till a planet passes between a star and their telescope’s line of sight. With mild from the star illuminating the planet from behind, they will use some easy physics ideas to determine the forms of molecules current within the planet’s ambiance.
In 2020, researchers realized they might use this system for planets orbiting white dwarfs. If such a planet had molecules created by dwelling organisms in its ambiance, the James Webb Area Telescope would in all probability have the ability to spot them when the planet handed in entrance of its star.
In June 2025, I published a paper answering a query that first began bothering me in 2021: May an ocean – seemingly wanted to maintain life – even survive on a planet orbiting near a lifeless star?
A universe stuffed with white dwarfs
A white dwarf has about half the mass of the Sun, but that mass is compressed into a volume roughly the size of Earth, with its electrons pressed as close together as the laws of physics will allow. The sun has a radius 109 times the dimensions of Earth’s – this dimension distinction implies that an Earth-like planet orbiting a white dwarf might be about the identical dimension because the star itself.
White dwarfs are extraordinarily frequent: An estimated 10 billion of them exist in our galaxy. And since each low-mass star is destined to ultimately develop into a white dwarf, numerous extra have but to type. If it seems that life can exist on planets orbiting white dwarfs, these stellar remnants may develop into promising and plentiful targets within the seek for life past Earth.
However can life even exist on a planet orbiting a white dwarf? Astronomers have known since 2011 that the habitable zone is extraordinarily near the white dwarf. This zone is the placement in a planetary system the place liquid water may exist on a planet’s floor. It might probably’t be too near the star that the water would boil, nor so far-off that it might freeze.
The liveable zone round a white dwarf can be 10 to 100 times closer to the white dwarf than our personal liveable zone is to our Solar, since white dwarfs are a lot fainter.
The challenge of tidal heating
Being so close to the surface of the white dwarf would bring new challenges to emerging life that more distant planets, like Earth, do not face. One of these is tidal heating.
Tidal forces – the variations in gravitational forces that objects in area exert on completely different elements of a close-by second object – deform a planet, and the friction causes the fabric being deformed to warmth up. An instance of this may be seen on Jupiter’s moon Io.
The forces of gravity exerted by Jupiter’s different moons tug on Io’s orbit, deforming its inside and heating it up, leading to lots of of volcanoes erupting always throughout its floor. Because of this, no floor water can exist on Io as a result of its floor is simply too scorching.
In distinction, the adjoining moon Europa can be topic to tidal heating, however to a lesser diploma, because it’s farther from Jupiter. The warmth generated from tidal forces has prompted Europa’s ice shell to partially soften, leading to a subsurface ocean.
Planets within the liveable zone of a white dwarf would have orbits shut sufficient to the star to expertise tidal heating, much like how Io and Europa are heated from their proximity to Jupiter.
This proximity itself can pose a problem to habitability. If a system has a couple of planet, tidal forces from close by planets may trigger the planet’s ambiance to lure warmth till it turns into hotter and warmer, making the planet too hot to have liquid water.
Enduring the crimson big part
Even when there is just one planet within the system, it might not retain its water.
Within the strategy of changing into a white dwarf, a star will develop to 10 to 100 occasions its authentic radius throughout the red giant phase. During that time, anything within that expanded radius will be engulfed and destroyed. In our own solar system, Mercury, Venus and Earth will be destroyed when the Sun eventually becomes a red giant before transitioning into a white dwarf.
For a planet to outlive this course of, it must begin out a lot farther from the star — maybe on the distance of Jupiter and even past.
If a planet begins out that far-off, it might have to migrate inward after the white dwarf has shaped as a way to develop into liveable. Computer simulations show that this kind of migration is possible, however the course of may trigger extreme tidal heating which will boil off floor water – much like how tidal heating causes Io’s volcanism. If the migration generates sufficient warmth, then the planet may lose all its floor water by the point it lastly reaches a liveable orbit.
Nonetheless, if the migration occurs late enough within the white dwarf’s lifetime – after it has cooled and is not a scorching, vibrant, newly shaped white dwarf – then floor water might not evaporate away.
Below the precise situations, planets orbiting white dwarfs may maintain liquid water and doubtlessly help life.
Seek for life on planets orbiting white dwarfs
Astronomers have not but discovered any Earth-like, liveable exoplanets round white dwarfs. However these planets are troublesome to detect.
Conventional detection strategies just like the transit technique are less effective because white dwarfs are much smaller than typical planet-hosting stars. In the transit technique, astronomers watch for the dips in light that occur when a planet passes in front of its host star from our line of sight. Because white dwarfs are so small, you would have to be very lucky to see a planet passing in front of one.
Nevertheless, researchers are exploring new strategies to detect and characterize these elusive worlds utilizing superior telescopes such because the Webb telescope.
If liveable planets are discovered to exist round white dwarfs, it might considerably broaden the vary of environments the place life would possibly persist, demonstrating that planetary programs might stay viable hosts for all times even lengthy after the loss of life of their host star.
This text is republished from The Conversation below a Artistic Commons license. Learn the original article.
