How real is the ice age threat in Project Hail Mary? | Science News

Added: 2026-04-30

[00:00:00]In Project Hail Mary, space-faring microbes called Astrophages start eating the sun, dimming it and many other stars.

[00:00:08]>> [music] >> The sun is dying.

[00:00:10]The movie suggests reducing the sun's luminosity by 10% [music] over 30 years would cool the planet by 10 to 15° C, plunging us into a new ice age. But, is that how ice ages happen? Not really.

[00:00:23]It's true that the sun's luminosity can change [music] and it's actually gotten brighter over time. 1 billion years ago, the sun was 10% [music] dimmer than now, but Earth was actually pretty warm because there was a lot of methane and carbon dioxide in the atmosphere, creating a greenhouse effect. There's also an 11-year solar cycle during which the sun dims and brightens, but that's only by about 0.1% and it doesn't really affect temperatures on Earth. Earth has had some serious [music] cold snaps, but those aren't related to the sun. It's more about atmosphere.

[00:00:53]Some really extreme icy periods were linked to big increases in rock [music] weathering that consumed greenhouse gases. Around 700 million years ago, for example, Earth's temperature plummeted to about -50° C.

[00:01:06]A lot of Earth's ice ages are also related to natural orbital cycles. Those are regular [music] changes in how elliptical Earth's orbit is or how much its axis is tilted toward the sun. Those cycles are tied, for example, to the last ice age [music] that hit its peak around 20,000 years ago when it was maybe 6° C colder than now.