They are Earth-like and Mars-like in terms of their oxidized iron.
There's no denying the fact that Earth is the only habitable planet and one of its kind, but according to new evidence there may be numerous Earth-like planets in the universe!
Researchers presented the findings in a new study published in the journal 'Science'.
"We have just raised the probability that many rocky planets are like the Earth, and there's a very large number of rocky planets in the universe," said co-author Edward Young, UCLA professor of geochemistry and cosmochemistry.
Led by Alexandra Doyle, a UCLA graduate student of geochemistry and astrochemistry, scientists developed a new method to analyze the elements in rocks from asteroids or rocky planet fragments that orbited six white dwarf stars.
White dwarf stars are dense, burned-out remnants of normal stars. Their strong gravitational pull causes heavy elements like carbon, oxygen and nitrogen to sink rapidly into their interiors, where the heavy elements cannot be detected by telescopes.
The closest white dwarf star Doyle studied is about 200 light-years from Earth and the farthest is 665 light-years away.
"By observing white dwarfs and elements present in their atmosphere, we are observing the elements in the body that orbited the white dwarf," Doyle said.
The data was collected by telescopes, mostly from the W.M. Keck Observatory in Hawaii.
"If I were to just look at a white dwarf star, I would expect to see hydrogen and helium. But in these data, I also see other materials, such as silicon, magnesium, carbon and oxygen -- material that accreted onto the white dwarfs from bodies that were orbiting them," Doyle explained.
When iron is oxidized, it shares its electrons with oxygen, forming a chemical bond between them, Young said.
"This is called oxidation, and you can see it when metal turns into rust. We measured the amount of iron that got oxidized in these rocks that hit the white dwarf. We studied how much the metal rusts," the researcher detailed.
Rocks from the Earth, Mars and elsewhere in our solar system are similar in their chemical composition and contain a surprisingly high level of oxidized iron, Young added.
Researchers said the oxidation of a rocky planet has a significant effect on its atmosphere, its core and the kind of rocks it makes on its surface.
"All the chemistry that happens on the surface of the Earth can ultimately be traced back to the oxidation state of the planet," Young said.
"The fact that we have oceans and all the ingredients necessary for life can be traced back to the planet being oxidized as it is. The rocks control the chemistry," he added.
Telling how alike were the rocks, Doyle said, "Very similar. They are Earth-like and Mars-like in terms of their oxidized iron."
The researchers studied the six most common elements in rock: iron, oxygen, silicon, magnesium, calcium and aluminium.
"If extraterrestrial rocks have a similar quantity of oxidation as the Earth has, then you can conclude the planet has similar plate tectonics and similar potential for magnetic fields as the Earth, which are widely believed to be key ingredients for life," Schlichting explained.