Too good to be true? Yes, it seems

One evening last week, I found myself wondering (god knows why) how long a “day” is on the other planets. A Google search to me to this NASA “science for kids” website, where I found this.

WHAT??? How the hell can a day on Venus be 5,832 hours long?  The NASA page had no useful explanation. (Although it does show kids how to make a graph.)

Much pondering of this question occurred during my walk with Joe the next day before he suggested seeing what ChatGPT had to say on the subject. 

Not long after I got home there was the following text exchange.

Joe: Me to CHATgpt: Please explain why solar day on Mercury and Venus is so much longer than Earth or other planets

ChatGPT:

The solar day is defined as the time it takes for a planet to complete one rotation on its axis and return to the same position relative to the sun. The solar day on Mercury and Venus is much longer than Earth and other planets because of their slow rotation rates.

Mercury has a very slow rotation rate, taking 59 Earth days to complete one rotation on its axis. This means that one solar day on Mercury is equal to 176 Earth days. Venus, on the other hand, rotates in the opposite direction to its orbit around the sun, making one solar day on Venus equal to 117 Earth days.

In contrast, Earth takes approximately 24 hours to complete one rotation on its axis, resulting in a solar day of 24 hours. Other planets like Mars, Jupiter, Saturn, Uranus, and Neptune have solar days that are closer in length to Earth’s solar day, with rotation periods ranging from just under 24 hours to several Earth days.

The reason for the slow rotation rates of Mercury and Venus is not entirely understood, but it is thought to be related to their proximity to the sun and their lack of large moons. The gravitational pull of the sun may have slowed down their rotation over time, while the lack of a large moon to stabilize their rotation may have also contributed to their slow rotation rates.

Me: Interesting. I did wonder about moons. “Venus rotates in the opposite direction…” Hmm.

Joe: 

All other planets spin anti-clockwise on their axis and orbit the Sun in an anti-clockwise direction. Venus also orbits the Sun anti-clockwise, but its unusual axis rotation is due to being upside down – it was knocked off its upright position earlier in its history!

Astronomers believe that at some point, a colliding celestial body tilted Venus so far off its original position that it is now upside down. The only other planet to spin in a weird direction is Uranus which spins on its side, probably the result of another collision early on in its life.

Joe: As I speculated gravitation pull of sun slows down the spin. Acts like a brake

Me: Slows it down a fuck of a lot. Five times slower than Mercury? Even if it’s upside down and going backwards…

Joe: 

However, this is not to say that Mercury experiences two sunrises in just over 58 days. Due to its proximity to the Sun and rapid speed with which it circles it, it takes the equivalent of 175.97 Earth days for the Sun to reappear in the same place in the sky. Hence, while the planet rotates once every 58 Earth days, it is roughly 176 days from one sunrise to the next on Mercury.

What’s more, it only takes Mercury 87.969 Earth days to complete a single orbit of the Sun (aka. its orbital period). This means a year on Mercury is the equivalent of about 88 Earth days, which in turn means that a single Mercurian (or Hermian) year lasts just half as long as a Mercurian day.

Now that’s weird! A Mercurian day is twice as long as a Mercurian year!!

Me:  Okay, my head hurts again

Joe: So Mercury orbits faster (88 days versus 365) because it’s so close to the sun, while actually rotating much slower (58 earth days vs 1 earth day).

A planet orbiting close to its star has a shorter year than a planet orbiting farther from its star.

Here is how long it takes each of the planets in our solar system to orbit around the Sun (in Earth days):

Mercury: 88 days

Venus: 225 days

Earth: 365 days

Mars: 687 days

Jupiter: 4,333 days

Saturn: 10,759 days

Uranus: 30,687 days

Neptune: 60,190 days

It takes Neptune 165 earth-years to make one orbit around the sun 

Well, that is fascinating, isn’t it?

Joe was so pleased with his findings that he posted them on Facebook with an acknowledgement that he was sure “a knowledgeable astrophysicist may find something to quibble about, but I was very pleased that it provided a rather complete synthesized answer to my specific question. Much more so than asking Google the same question and having to read several suggested links that did not address my request. ChatGPT 1, Google 0.”

I saw the post and, as someone else was writing a reply, I also wrote one: “After spending a good chunk of time during our walk pondering how it could take the equivalent of 5000+ Earth days for a solar day on Venus, it was amazing that you were able to get a quick and comprehensible answer.”

No sooner had I left my comment than the long one that was being written by our friend Tom, who is a scientist (though not an astrophysicist), popped up.

His take? “This is 100% trivial, incoherent, or wrong. But it sounds good enough to fool you, and you’re no dummy. This is a real problem!

“‘The solar day on Mercury and Venus is much longer than Earth and other planets because of their slow rotation rates.’Translation: the day is longer because the day is longer.

“‘Mercury has a very slow rotation rate, taking 59 Earth days to complete one rotation on its axis. This means that one solar day on Mercury is equal to 176 Earth days.’ Translation: 59 is equal to 176. (176 is the correct number… point to Google.)

“’Venus, on the other hand, rotates in the opposite direction to its orbit around the sun, making one solar day on Venus equal to 117 Earth days.’ Translation: If clauses are strung together people will feel like an explanation has been provided even though one hasn’t. (The day on Venus is 243 Earth days. Point to Google.)

“’Other planets like Mars, Jupiter, Saturn, Uranus, and Neptune have solar days that are closer in length to Earth’s solar day, with rotation periods ranging from just under 24 hours to several Earth days.’ Translation: Facts are social constructs! (None of the planets beyond the inner three have a day longer than 24 hours. Another point to Google!)

“’The reason for the slow rotation rates of Mercury and Venus is not entirely understood, but it is thought to be related to their proximity to the sun and their lack of large moons. The gravitational pull of the sun may have slowed down their rotation over time, while the lack of a large moon to stabilize their rotation may have also contributed to their slow rotation rates.’ Translation: GIF of Basil Fawlty saying, ‘Don’t mention the tides!’ (Tidal forces explain Mercury’s slow rotation. Nobody know WTF is going on with Venus… there is modelling of the early solar system that shows it’s relatively easy to get the distribution of planetary orbits we see if Jupiter and another giant planet formed close to the sun, and then their mutual gravitational interaction resulted in one of them being ejected from the solar system while Jupiter got kicked out to where it is now. We see some extra-solar systems with “hot Jupiters” still in place, very close to their primary. These early shenanigans may have resulted in the retrograde rotation of Venus, which is otherwise inexplicable. I didn’t Google any of that… dynamical modelling of the solar system is an interest of mine.)

“So, I’d say it’s Google 3, ChatGPT -3. This is the problem with this tech: it generates answers that sound plausible to an intelligent, well-educated, non-expert that are completely wrong.

“These are not quibbles: ChatGPT failed to answer the question and gave a bunch of information that is false. And it did so in a way that fooled someone who is smarter and more educated than at least 90% of the population.

“Any answer to why the days on Venus and Mercury are shorter than Earth days that doesn’t mention tides is wrong. Tides – which include deformations of planetary crusts and pushing around liquid in the inner core if a planet has one – tend to slow rotation. The reason why we only see one side of the Moon is that tides slowed it down and stopped it. This is called being ‘tidally locked’, which is what Mercury was assumed to be before the early missions to explore the solar system.

“Generically, for sure ‘stronger gravitational forces’ is in the right ballpark, but it’s specifically tidal forces, which go as 1/r**3 rather than the 1/r**2 of point-like gravitational attraction, that are important. ChatGPT missed that completely.”

To which Joe replied: “I knew it was too good to be true/precise. But it did provide the ‘generic’ answer that I couldn’t find elsewhere (perhaps I didn’t dig enough). Guess it’s good at synthesizing ‘plausible’ sounding answers, that most people are ill equipped to refute … not unlike what Google gives us.”

I can’t pretend I fully understood Tom’s response/assessment, although I felt as if I was more or less following it, until I got to “go as 1/r**3 rather than the 1/r**2 of point-like gravitational attraction”. 

Which was when I commented: “Oh, well, as I was writing so was Tom and now I am back to having no idea.”

Even with her glasses on Georgie can’t figure it out either.

During our walk, before the ChatGPT suggestion, we decided what was needed was a 1-800 number for Bill Nye – or, even better, Neil DeGrasse Tyson. I still need that.