The Jupiter Trojans are two clusters of asteroids that orbit the sun about 60 degrees ahead, and 60 degrees behind, Jupiter. Those are the L4, L5 points and the two groups are called The Greek Camp and The Trojan Camp.

There are probably hundreds of millions of the things, approximately a million of which are greater than 1 km in diameter. Only about 7000 have been observed and described. Some of them are binaries or in even more complex systems.

They were first discovered some 100 years ago. The biggest of them is 624 Hektor, about 400 km long, situated at L4 (the so called Greek camp). I have no idea why “Hektor” is in the Greek camp. It has a satellite, about 100 km across.

617 Patroclus is also in the wrong camp, the Trojan camp. That’s the largest in that camp, and it also has a satellite.

The Jupiter Trojans are dark. Hektor for instance has an albedo of about 3%. That is, it reflects only 3% of light. They might be coated in tholins, a sticky organic goo.

Anyway, there is a mission called Lucy which is going to visit both camps. It will be the first mission to the Jupiter Trojans.

Lucy will launch in 2021, at arrive at L4 in 2027 where it will perform flyby encounters with four of these asteroids. It will then return to the vicinity of Earth, receive a little gravity kick to speed it towards L5, where it will run a flyby of 617 Patroclus in 2033.

So that’s nice.

There are only three pieces of science hardware:

high-res visible-light imager, based on the LORRI imager on New Horizons
colour imager and infrared spectrometer, based on the Ralph imager on New Horizons
thermal infrared spectrometer, based on that used by the OSIRIS-REX mission

dv said:

The Jupiter Trojans are two clusters of asteroids that orbit the sun about 60 degrees ahead, and 60 degrees behind, Jupiter. Those are the L4, L5 points and the two groups are called The Greek Camp and The Trojan Camp.

There are probably hundreds of millions of the things, approximately a million of which are greater than 1 km in diameter. Only about 7000 have been observed and described. Some of them are binaries or in even more complex systems.

They were first discovered some 100 years ago. The biggest of them is 624 Hektor, about 400 km long, situated at L4 (the so called Greek camp). I have no idea why “Hektor” is in the Greek camp. It has a satellite, about 100 km across.

617 Patroclus is also in the wrong camp, the Trojan camp. That’s the largest in that camp, and it also has a satellite.

The Jupiter Trojans are dark. Hektor for instance has an albedo of about 3%. That is, it reflects only 3% of light. They might be coated in tholins, a sticky organic goo.

Anyway, there is a mission called Lucy which is going to visit both camps. It will be the first mission to the Jupiter Trojans.

Lucy will launch in 2021, at arrive at L4 in 2027 where it will perform flyby encounters with four of these asteroids. It will then return to the vicinity of Earth, receive a little gravity kick to speed it towards L5, where it will run a flyby of 617 Patroclus in 2033.

So that’s nice.

There are only three pieces of science hardware:

high-res visible-light imager, based on the LORRI imager on New Horizons
colour imager and infrared spectrometer, based on the Ralph imager on New Horizons
thermal infrared spectrometer, based on that used by the OSIRIS-REX mission

This is a definite go-ahead.

The weirdest thing about it is that they’re visiting both Trojan points, which requires returning to Earth part way through the mission. Why bother? Can’t they get a good idea of how the Trojan asteroids formed from just one Trojan point.

One thing I didn’t know until a few days ago is that there’s quite a lot of difference between asteroids at the same Trojan point, which is interesting and suggests to me that they were captured after the formation of Jupiter. They would be more interesting if they held lumps of matter from the interior of Jupiter, scattered off when Jupiter was forming.

Each encounter will be a flyby, not an extended look.

mollwollfumble said:

The weirdest thing about it is that they’re visiting both Trojan points, which requires returning to Earth part way through the mission. Why bother? Can’t they get a good idea of how the Trojan asteroids formed from just one Trojan point.

Point taken but no complaints from me.

dv said:

mollwollfumble said:

The weirdest thing about it is that they’re visiting both Trojan points, which requires returning to Earth part way through the mission. Why bother? Can’t they get a good idea of how the Trojan asteroids formed from just one Trojan point.

Point taken but no complaints from me.

Why back to Earth, couldn’t Mars be used for the gravity assist?

sibeen said:

dv said:

mollwollfumble said:

The weirdest thing about it is that they’re visiting both Trojan points, which requires returning to Earth part way through the mission. Why bother? Can’t they get a good idea of how the Trojan asteroids formed from just one Trojan point.

Point taken but no complaints from me.

Why back to Earth, couldn’t Mars be used for the gravity assist?

Two points:

1/ It’s going to be coming back to the Earth’s vicinity anyway. Its initial loop is just a big ellipse.

2/ Mars has only 10% of Earth’s mass so it’s a weaker assistant.

dv said:

sibeen said:

dv said:

Point taken but no complaints from me.

Why back to Earth, couldn’t Mars be used for the gravity assist?

Two points:

1/ It’s going to be coming back to the Earth’s vicinity anyway. Its initial loop is just a big ellipse.

2/ Mars has only 10% of Earth’s mass so it’s a weaker assistant.

Yeah, but surely we can be way more adventurous with Mars. Get way, way closer; barely skim the suface.

Another brag from the NASA website:

“No other space mission in history has been launched to as many different destinations in independent orbits around our sun.”

Ha.

dv said:

Another brag from the NASA website:

“No other space mission in history has been launched to as many different destinations in independent orbits around our sun.”

Ha.

what about the voyagers?

JudgeMental said:

dv said:

Another brag from the NASA website:

“No other space mission in history has been launched to as many different destinations in independent orbits around our sun.”

Ha.

what about the voyagers?

Well now by my count, Voyager 2 visited Jupiter, Saturn, Uranus and Neptune.

Lucy will be visiting 5 bodies.

dv said:

JudgeMental said:

dv said:

Another brag from the NASA website:

“No other space mission in history has been launched to as many different destinations in independent orbits around our sun.”

Ha.

what about the voyagers?

Well now by my count, Voyager 2 visited Jupiter, Saturn, Uranus and Neptune.

Lucy will be visiting 5 bodies.

close but no cigar eh?

This animation shows the motion of the Trojans relative to the Sun-Jupiter pair, and it is kind of hypnotic.

dv said:

This animation shows the motion of the Trojans relative to the Sun-Jupiter pair, and it is kind of hypnotic.

Space starlings.

AwesomeO said:

dv said:

This animation shows the motion of the Trojans relative to the Sun-Jupiter pair, and it is kind of hypnotic.

Space starlings.

a murmuration of tojans.

dv said:

This animation shows the motion of the Trojans relative to the Sun-Jupiter pair, and it is kind of hypnotic.

I like it.

Trojans also go by the name of tadpoles, from the shapes of their orbits.

Nice.

There’s another set that kiss the Trojans and also the anti-Jove, called the Hildas.

Ah we’ll get to them.

Made me wonder, hey, are there any Earth Trojans?

And the answer is that there has been exactly one such discovered, a rock at the Sun-Earth L4 point called 2010 TK7, less than 1 km across.