Breaking space news, the latest updates on rocket launches, skywatching events and more! Contact me with news and offers from other Future brands Receive email from us on behalf of our trusted partners or sponsors By submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. "Artificial satellites, even those invisible to the naked eye, can obstruct astronomical observations that help detect asteroids and understand our place in the universe," Robert McMillan, research professor of astronomy emeritus at the University of Arizona and one of the letter's authors, said in an emailed statement. "The potentially long-term environmental harms of deploying tens of thousands of satellites are still unclear." Harvard University celebrity astrophysicist and extraterrestrial life researcher Avi Loeb is among the signatories of the letter. So are Jonathan McDowell, a leading space debris expert, satellite tracker and astronomer at Harvard Smithsonian; David Jewitt, the discoverer of the first Kuiper Belt object and distinguished professor of astronomy at UCLA; and space environmentalist Moriba Jah. The U.S. nonprofit Public Interest Research Group (PIRG) conceived the letter following the release of its report detailing the potential hazards of satellite mass incineration in August. PIRG estimates that when megaconstellation deployment reaches its peak, some 29 tons of metallic waste will be vaporizing in Earth's atmosphere every day, the equivalent of "a car falling from space" every hour. Satellites are mostly made of aluminum, which forms aluminum oxide when burnt. Aluminum oxide, or alumina, contributes to ozone depletion and can alter the atmosphere's ability to absorb heat, thus affecting Earth's climate. Satellite reentries also produce nitrogen oxides, which, too, are known to damage ozone. Illustration of a satellite burning up during reentry. (Image credit: ESA)