As we rejoice the Earth finishing another lap around the Sun, let’s take a moment to picture what life would be like in a world lacking years – a world that somehow stopped to orbit its star. Certainly, it’s a strange question, but its’s one that I’ve been enthusiastically wondering about lately. Not because it’s of any specific relevance, but simply because it’s hilarious (at least to me) and fun to think about.

What would happen to us if a huge space finger were to smoothly stop the Earth in its orbit?

Nothing good.

Here, try it out for yourself. Press ‘start’ in the animation below (made by Michael Dubson and the assosiates at Phet Interactive Simulations / University of Colorado). You should perceive a planet revolving around the Sun.

Now press ‘reset’, and drag the circle with the letter ‘v’ to lessen the planet’s speed. Then press ‘start’ another time. What happens? (While you’re having fun with this, you may enjoy trying out some of the different situations in the drop-down menus, and observing the gravitational ballet that follows.)

If you decelerated the planet sufficiently, you should see it smashing into the Sun.

To see why, let’s first recall why things stay in orbit. Every child seeing at the sky has at some point questioned, “why doesn’t the moon fall down?” The answer is handsomely simple, yet it took a mind as bright as Isaac Newton’s to work it out. (Maybe a sign of brilliance is coming up with simple answers to children’s queries.)

Newtons’ reaction to the child’s query would have been – the moon does fall. It’s continuously falling. Being in orbit is a state of always falling, and continuously missing what you’re falling towards. In The Hitchiker’s Guide to the Galaxy, Douglas Adams defines the secret to flight. “The knack”, he marks, “lies in practicing how to throw you at the ground and miss”. As it turns out, this is also a great explanation of what it means to circle something.

Here’s how Newton described it. Picture a cannonball is fired from a altitude. If you fire the cannonball with more speed, it’ll travel further before it smashes on the ground. The faster the cannonball, the larger it travels.

But wait – the Earth is round. That means that if you shoot the projectile with sufficient speed, then by the time it would have hit the ground, it’s travelled far enough that the ground has bent away underneath it. So the cannonball carry on to fall to the ground, and the ground carry on to curve away from it. It’s now in a state of continuous free fall – the cannonball is in orbit!

(Newton’s impression is masterfully clarified in this wonderful Radiolab segment.)

So the only thing that creates an orbit different from plain-old falling is having sufficient speed to miss the thing you’re falling to. Think releasing a cannonball with zero speed against shooting it into orbit. And for the same reason, if the Earth were raided of all of its orbital speed, it would fall straight into the Sun. It would no longer have the speed it requires to miss the Sun.

How much time would this ‘Earthfall’ take?

(If you recall some high school physics and want find out the answer for yourself, here’s a clue for resolving it without any calculus.)

I’ll skip the math, but it turns out that we’d have 64 and a half days before we rushed into the fiery pits of the center of the Sun. But don’t worry; we’d be pretty dead before that takes place.

As the Earth drops towards the Sun, it gains speed. The more it falls, the more strong the sunlight, and so Earth begins to heat up.

Here’s a graph of the Earth’s average temperature over these 64 and a half days.

If we zoom out, we see that most of the act occurs in Earth’s last day.

You can get that things are going to get very rough soon enough.

Let’s take this flight of fancy one step ahead, and suppose what things would be like on Earth as it drops into the Sun. What comes is my shot at a science-based play-by-play of Earth’s final 64 and a half days.

Day 0

We start our drop towards the Sun.

Day 6

After 6 days of dropping towards the Sun, the Earth’s temperature has increased by around 0.8 degrees Celsius. That’s the same extent by which we’ve risen our planet’s temperature ever since 1880. You may not sense the heat as yet, but you will soon.

Day 21

The average worldwide temperature has now increased by around 10 degrees Celsius, to 35 C (95 F). The planet is now suffering a very intense global heat wave, whose temperature increase rivals the record-breaking 2003 European heat wave. Crops are starting to fail.

Day 35

It’s been over a month of Earth fall, and we’re now 20% of the way to the Sun. The Sun is intolerably bright and strong, and remarkably larger in the sky. At 58 C (137 F), the average worldwide temperature now surpasses the historic warmest temperature documented on Earth, which was 56.7 C (134 F) witnessed in Death Valley, CA.

For most people on the planet, it’s now difficult to stay alive without air conditioning, and the electricity structure is either tapped out or dying. Forest fires are devastating through the wilderness. Land animals that can’t hole in to the soil to get break from the heat are going extinct. The insects, too, are feeling the heat and dying out. The cumulative water temperature will cause fish to start dying out, as warmer water has less oxygen and more ammonia (which is toxic to fish), and as the whole marine food chain would be disturbed and failing.

It’s so hot that even the Saharan silver ant, one of the most heat resilient land animals on Earth, can no longer endure the heat (for it can stay alive up to 53.6 C). Though, the Sahara desert ant is prospering – it can endure surface temperatures of up to 70 C. As scavengers, these ants nourish on the bodies of other creatures that have died from the heat, and there’s now adequate of food to go around.

Day 41

We’ve now overlapped Venus’s orbit. The average temperature surpasses 76 C (169 F), a temperature too hot for even the Sahara desert ant.

The Pompeii Worm, though, is still holding on. These amazing beings grow up to 13 centimeters (5 inches) long, and are known to endure temperatures of up to 80 C. It’s supposed that they owe this heat-resisting superpower to a shielding “fleece-like” layer of bacteria on their backs, which shields them from the heat. These worms are “the most heat-tolerant composite animal known to science”, with the exclusion of tardigrades (whom we’ll hear from shortly).

Day 47

We just left the inhabitable zone, that Goldilocks area of a solar system (not too hot, not too cold) proficient of supporting life as we know it.

At 103 C (217 F), the ambient temperature now surpasses the boiling point of water. The Earth’s oceans are boiling. Liquid water can no longer be on much of Earth’s surface and steam covers the planet. Most life on Earth is destroyed by now, mainly complex life forms, even the astonishingly heat-resistant Pompeii Worm. Hyper thermophiles (such as heat-resistant bacteria) are alive (perhaps even thriving) deeper in the ocean where the water pressure stops boiling. Fire charitable plants are still holding on.

Tardigrades (or water bears) take the prize for the hardest known living things. Heck, these creatures have even endured in the vacuum, great cold and high radiation of outer space for a whopping 10 days. Really, they are among Earth’s extreme survivors.

At this point, the Tardigrades are possibly just beginning to notice that something is awry. They’re maybe bunkering down by hanging their metabolism, curling up and dehydrating themselves into a dry state that comprises only 1% of their original water. In this dehydrated state, called a tun, they can stay alive and asleep for nearly a decade.

Day 54

Goodbye, dear tardigrades. You survived us all. Although you can bear a madly inspiring temperature range, from near absolute zero to 151 C, Earth’s temperature now surpasses 160 C, too hot even for you.

Day 57

We’ve crossed Mercury’s orbit, and are now the nearby planet to the Sun, a difference that we will hold for another week. The ambient temperature surpasses 200 C.

Day 64

The Earth is now in its concluding day. As of the Earth’s gigantic accumulated speed, and the strong gravitational force of the nearby Sun, we’ll cover the last 7% of our voyage’s length by 1 pm today. The Sun’s gravity is now so extreme, that it pulls the front of the Earth with expressively more force than the back of the Earth. This variance gravity, or tidal force, is extending Earth out into an oval shape. Magma explodes all over cracks and fissures in the planet’s crust.

The day starts off at a balmy 800 C, with the Sun fourteen times its normal size in our sky. By noon the temperature hits 2000 C, more than hot sufficient to melt rock. Earth’s surface fluxes into magma.

At half past noon, we’ve nearly at home. The Sun is so close that it fills most of the day sky. The Earth is crossing a made-up line of no return called the Roche limit. This is the point where the gravitational forces drawing Earth apart surpass Earth’s ability to hold it together. As it crosses this critical radius, the tidal effect of gravity tears the Earth into minor balls of magma and melting rock.

And this is how our crumbling planet finally meets the end of its expedition to the Sun. I hope you liked the trip.
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