We’re circling the Sun at a rate of between 18.20–18.83 miles per second. It is not a fixed speed because Earth travels on an ellipsis, and moves a hair faster when it’s closer to the Sun than it does when further away. It averages out to about 67,000 miles per hour over the course of the year. At that speed, a full revolution is 365 days, 5 hours, 48 minutes, and 46 seconds in the making. At least for now.
Each year, Earth’s voyage around the Sun takes just a little bit longer, to the tune of roughly 3 nanometers per second. It’s minuscule, but adds up over time. Since the solar system’s inception 4.571 billion years ago, Earth is moving 22 mph slower.
The main reason is that Earth is drifting ever so slightly away from the Sun, stretching out the orbital path, and lengthening the duration of a revolution.
We’re not fleeing the Sun so much as it’s pushing us away. As the Sun’s hydrogen core transmogrifies into helium through the process of nuclear fusion, the Sun loses somewhere in the neighborhood of 4 million tons of mass every second. Since that process began billions of years ago, the Sun has lost mass equivalent to 1 Saturn, or approximately 95 Earths if you prefer to think about it in homier terms. The Sun also suffers particle loss through Solar Wind, and that has resulted in its shrinking by another 30 Earths or so. Solar flares and coronal mass ejections also steal away mass. In all, the Sun is ~1027 kg lighter than it was at the birth of our Solar System. Here’s what 1027 looks like written out in digits:
1,000,000,000,000,000,000,000,000,000
Since a ton equals two-thousand, feel free to add another three zeroes and flip that one to a two. Then again, a gram ain’t much, so maybe just leave it as is, stare at it a bit, and try to feel the full weight of it.
Some of the mass that the Sun spits out slams into our planet after flying through space for around three days. These solar whacks push Earth away from the Sun by just over half an inch each year. It doesn’t sound like much, but Earth is now about 50,000 km (<31,000 miles) further away from the Sun than it was 4.5 billion years ago.
We all slow down as the years pass, mortality dancing in our eyes. You’ll die eventually. So will I, and everyone else. The Sun and Earth too are doomed.
As with you, me, and all mortal creatures, ultimate reckoning might come for Earth quickly through unforeseen events, or it might slowly reach an inevitable conclusion.
Some large object might come hurling across the galaxy, collide with us, and end it all in the universe’s version of a car crash. No seatbelts, no air bags. Boom.
Something akin to a major stroke is the roughly 1% chance that over the next billion years, the solar orbit of one of the four inner planets (Mercury, Venus, Earth, Mars) will destabilize. If that happens, Earth is done. Even if our own orbit remains stable, another inner plant’s orbital destabilization would unleash such havoc that Earth will either crash into the Sun or shoot out of the solar system altogether.
I’m rooting for the former; I’d always rather be too warm than too cold.
The best we can hope for is “natural causes.” If we dodge catastrophes near and far, and our solar system manages to live out its full duration, the Sun will eventually heat up, and life on Earth will become untenable. What’s more, as the process continues and the Sun become a Red Giant, it will expel yet more mass. This will result in Earth’s orbital path slinging outwards by 10–15%, and the speed of its revolution decreasing by a similar percentage. Solar expansion will continue until Helios swallows Mercury and Venus, like some ancient Greek god devouring its children. Earth itself will crash into the remnants of the Sun in ~1026 years, give or take.
I’d write out 1026 , but it’d just seem anti-climactic.
As for now, I guess we can all agree to call pretend that we’re witnessing Earth’s 2024th trip around the Sun. Yes, yes, we tell ourselves, as of the middle of last night, it is the year 2024.
Or 7421 (Chinese). Or 6774 (Assyrian). Or 5784 (Hebrew). Or 5137 (Mayan). Or 5124 (Hindu, Kali Yuga). Or 4356 (Korean). Or 2777 (Ancient Roman). Or 2568 (Buddhist). Or 1945 (Balinese). Or 1445 (Islamic). Or 1431 (Bengali). Or 1024 (Igbo)
Or, if we’re really being honest, whatever the numerical designation, perhaps we’ll just call it t-minus Red Giant
Either way, let’s see if we can make it another 365.2422 days. If not, we shouldn’t say we didn’t see it coming.
This essay originally appeared a 3 Quarks Daily. A quark is ~10−18 m.