Both Venus and Mercury can be the closest planet depending on the orbit (Mercury is actually the closer for longer one, though Venus gets closest). But can Mars ever be the closest?
Well here are the average distance from the sun for the first four planets:
- Mercury: 36 million miles
- Venus: 67 million miles
- Earth: 93 million miles
- Mars: 142 million miles
So if it happens that Mercury and Venus are both on the far side of the sun from the Earth, and Mars is on the same side, Mars could be as close as 49 million miles. While Mercury could be as far as 129 million miles and Venus could be as far as 160 million miles. Give or take, considering those are average distances.
I don’t know if they ever line up like that, though. That would take a lot more orbital mechanics or star charts than I’m willing to put into it.
So, as @Chingon’s link shows, at this moment, Mars is the closest planet to Earth, by quite a fair amount – 3.6 light minutes to Mars, vs. 8.5 light minutes to Venus, and 9.3 to Mercury.
And Mars will be even closer on Oct. 6, 38 million miles = 3.4 light minutes.
However, Mercury is actually the planet that spends most time closest to the Earth.
You’d need orbital mechanics if you wanted to know WHEN they’d line up like that. But it the question is “if they ever”, then the answer is surely “yes, eventually”.
That would not have occurred to me, but now that you said it, it makes a lot of sense. Here’s my “back of the envelope” calculation:
Mercury is so close to the sun, and has such a short year, that the line from Sun to Mercury to Earth will be fairly close to a straight line almost half the time. But even when Venus and Mars are on the same side of the Sun as we are, most of that time it is nowhere near a straight line, so Mercury would win (probably even if it happens to be on the other side).
I hadn’t done it on an envelope but I could see in my own head how little Mercury whizzes round whilst Venus and Mars lumber around on the far side of the sun. With them two out of the picture for a decent chunk of the year I could see how plausible it became.
The maths is well beyond me though, as was even the envelope, I just squinted and thought “yeah, could be”
I’ve always understood the statement that Venus’ is closest to Earth to simply mean that its orbit is the closest to ours, not that the planet itself is always literally closer.
What would take more energy, getting a rocket to Mercury or Venus?
The exact fuel requirements/launch window will depend on a number of factors, but it is easier to get from here to Venus than to get to Mercury, even though getting to Mercury might take less time.
The math behind orbital mechanics is dominated by delta V, not distance. In fact the distance is usually determined by the amount of delta V you’re willing to spend. Objects close to the Sun (like Mercury) move fast, and is one of the most difficult places in the solar system to get to on a direct route. Getting into orbit is even harder because the planet does not support aerobraking (probes to Venus or Mars can use the atmosphere to perform the orbital insertion with minimal extra propellant). On the other hand, gravity assists are possible. The Messenger probe (to Mercury) performed two gravity assists on Venus and a few more on Mercury itself. It took much longer than a direct transfer would have, but was far more efficient.
The tricky thing about a spacecraft mission to Mercury isn’t so much the fuel needed to get there, it’s slowing down once you arrive. That’s why a mission to Venus can use a simple transfer orbit, whereas all of the Mercury orbiters have used complicated gravity assist manuevers with the Earth and Venus.
Wait, Mercury is the closest to Earth on average?
Explain, please since it’s orbit is inside Venus?
https://blogs.socsd.org/aobrien/science-2/curiosity-rover/shortest-distance-from-planets-to-earth/
The distance between Venus and Earth varies depending on where the two planets are in their orbits. At their closest, the gap between them is 38 million kilometers, and at their furthest, 261 million kilometers.
It varies by the orbital position of the two planets. The average is about 26 million miles and the closest is about 24 million miles.
Mercury is an average distance of 48 million miles (77 million km) from Earth.
The distance from Mercury to the Earth varies greatly as both planets orbit the Sun. At its closest approach, Mercury is about 77 million kilometers (48 million miles) from Earth; at its furthest, about 222 million kilometers (138 million miles).
Ah but I see, on that other cite:
In the commentary, the researchers devised a new mathematical technique, called the point-circle method, to measure the distances between planets. This method averages the distance between a bunch of points on each planet’s orbit, thereby taking time into consideration. When measured that way, Mercury was closest to Earth most of the time. Not only that, but Mercury was also the closest planet to Saturn, and Neptune, and all of the other planets. The researchers checked their findings by mapping out where the planets were in their orbits every 24 hours for 10,000 years.
However, not everyone agrees with this new definition of “closest” planet.“Suppose you live in a house where the people who live next door to you spend half the year someplace, maybe you live in Wisconsin and your nearest neighbors spend seven months of the long winters in Florida,” said Steven Beckwith, the director of the Space Science Laboratory and professor of astronomy at UC Berkeley, who was not part of the commentary. “During the winter, the people in the next house over would be closer to you.”
But most people would still say that their closest neighbors are the ones who live immediately next door for the rest of the year, Beckwith told Live Science. “It is an interesting way of redefining ‘closest,’ but it is hardly profound.”
Interesting discussion.