More than 100 billion ‘rogue planets’ could be floating about in the Milky Way, according to new research.
The free floating worlds are unattached to any sun – meaning they drift aimlessly through space.
A NASA mission is now planning to count just how many there are – and the figure will be mind-boggling. The study predicts they will outnumber the stars in the galaxy – shedding fresh light on its evolution.
Described as a “totally new frontier” in the exploration of space, it will be able to spot planets as small as Mars.
Co author Professor Scott Gaudi, an astronomer at Ohio State University, said: “The universe could be teeming with rogue planets – and we wouldn’t even know it. We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.”
The Nancy Grace Roman Space Telescope is set for lift off in the next five years. It will create enormous panoramic pictures in unprecedented detail. Its wide field of view will enable sweeping cosmic surveys – yielding a wealth of new information.
Free-floating – or rogue – planets have been known about for decades. But their prevalence is a mystery. Our sun has at least eight – and most other stars have some.
Simulations by Prof Gaudi and colleagues found the revolutionary telescope will detect hundreds.
This will infer they are more common than stars – of which there are at least 100 billion in the Milky Way. They will be too cold to harbour life.
(Image: Skórzewiak / stock.adobe.com)
The isolated objects are similar in size to conventional planets – and too cold to harbour life. Their origin is unknown. One theory is they were previously bound to a host star – before hurtling into interstellar space.
It is hoped the telescope – named after a female astronomer hailed the ‘mother’ of Hubble – will build the first census of them. This will help explain how they formed. It will also search for planets that do orbit stars.
They may take shape in the gaseous disks around young stars – similar to those still bound to their host stars. Ejection may follow through interactions with other planets in the system – or even ‘fly-bys’ by other stars.
Another hypothesis is they are born when dust and gas swirl together – just like stars.
The telescope is designed to test these models. The study found it is likely to be ten times more sensitive to these objects than current ground based telescopes.
It will focus on planets between our sun and the centre of the Milky Way where a supermassive black hole lives – covering some 24,000 light years.
Lead author Samson Johnson, a graduate student in Prof Gaudi’s lab, said: “There have been several rogue planets discovered.
But to actually get a complete picture, our best bet is something like Roman. This is a totally new frontier.”
Rogue planets have historically been difficult to detect. Astronomers discovered planets outside Earth’s solar system in the 1990s.
Those planets, called exoplanets, range from extremely hot balls of gas to rocky, dusty worlds. Many of them circle their own stars, the way Earth circles the sun.
But it is likely that a number of them do not. And though astronomers have theories about how rogue planets form, no mission has studied those worlds in the detail that Roman will.
The mission will search for rogue planets using a technique called gravitational microlensing.
It relies on the gravity of stars and planets to bend and magnify the light coming from other stars that pass behind them from the telescope’s viewpoint.
The effect is linked to Albert Einstein’s Theory of General Relativity. It is only visible for a short period of time – once every few million years.
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As rogue planets are located on their own, without a nearby star, the telescope must be highly sensitive to the magnification.
It can find planets thousands of light-years away from Earth – much farther than other planet-detecting methods.
The study published in Astronomical Journal estimates the mission will be able to identify rogue planets the mass of Mars or larger.
Mars is the second-smallest planet in our solar system and is just a little bigger than half the size of Earth.
They are unlikely to support life. Johnson said: “They would probably be extremely cold, because they have no star.”
But studying them will help scientists understand more about how all planets form.
Mr Johnson added: “If we find a lot of low-mass rogue planets, we will know as stars form planets, they are probably ejecting a bunch of other stuff out into the galaxy. This helps us get a handle on the formation pathway of planets in general.”
Other research missions involving Ohio State astronomers will search for exoplanets that could host life.
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