“These two papers reinforce each other tremendously, and I think their story is becoming really compelling,” says Alessandro Morbidelli, a planetary scientist at the Côte d’Azur Observatory in Nice, France, who was not part of either research team.
The four planets closest to the sun — Mercury, Venus, Earth and Mars — all formed in the inner part of the solar nebula, the disk of gas and dust that spun around the newborn sun. The solar nebula’s inner region was so dense that friction heated it enormously, drying it out. Many researchers have therefore proposed that Earth got its water only after ice-bearing asteroids and comets born far from the sun hit Earth.
In 2020, however, researchers reported a surprise: Hydrogen exists in rare meteorites known as enstatite chondrites, which resemble our planet’s building blocks (SN: 8/27/20). The discovery suggested that Earth’s building blocks possessed plenty of hydrogen right from the start, cosmochemist Laurette Piani of the University of Lorraine in Vandœuver-lès-Nancy, France, and colleagues found.