# Tag Info

98

The comet's tail always points away from the Sun. Yes, even when the comet is heading back into the outer solar system. This is because the tail isn't a 'trail' of where the comet has been, like a rocket exhaust or contrail, but instead it's gas, ice and other debris blown off by the stellar wind. (There's actually two tails, one made of charged particles, ...

55

Your assumptions are incorrect. A space ship (once it has escaped Earth) will also continue travelling - in fact it will only need fuel to change its trajectory and velocity outwith gravitational effects from other bodies. You will need sufficient fuel or power for life support, if you have a crewed ship, and a reserve of fuel to manoeuvre at your ...

26

Ulysses, the shuttle-launched joint NASA/ESA probe to study the sun's polar regions, ran through three comet tails, more or less by chance. Ulysses Catches Record for Catching Comets by Their Tails ...comet Hyakutake ...On May 1, 1996, while Ulysses was cruising through space studying the solar wind, its data suddenly went wild for a few hours. The once-...

17

Spaceships will keep travelling in their orbits just the same as comets or asteroids, without fuel. The exception is that spacecraft in low orbit are affected by the upper fringe of the atmosphere, and need a slight boost every few months. Spaceships need fuel to change their course or to fly from the ground into space and back. Typically they only run their ...

16

The harpoons are intended to hold the lander to the surface long enough to get the ice screws on the lander's legs in securely. The ice screws are intended as the more permanent hold-down solution. Bear in mind that the comet offers essentially no gravity; imagine trying to drive a wood screw into the ceiling without pushing the screwdriver upward at all. ...

16

There isn't any limit to how small bodies can orbit each other (gravity-wise) until you get to atomic scale where one of the remaining three fundamental forces (weak force, strong force and electromagnetism) take over and gravity becomes largely irrelevant. With smaller bodies, gravitational potential will only be that much smaller and required centrifugal ...

15

While those movies probably do it because that's how comets are commonly depicted, it might not be that inaccurate. Remember that the Earth itself is moving around the Sun, so if a comet is heading for Earth, that means it's heading for a point where Earth will eventually be, not where it currently is. It would therefore be possible to see such a comet be &...

15

If you're the comet, the way to hit Earth is not to head directly for it. That's because Earth is orbiting the sun: you need to aim at where Earth will be, not where it is right now. For example: By Phoenix7777 - Own work Data source: HORIZONS System, JPL, NASA, CC BY-SA 4.0, Link This shows a transfer orbit from Earth (blue) to Mars (green), but the basics ...

15

Rosetta collected dust from 67P/Churyumov-Gerasimenko and analyzed it under an atomic force microscope, without landing on the cometary body itself; depending on your definitions this would seem to imply having flown through its tail. Navigation isn't much of an issue; you simply navigate close to the cometary body and hang out on the sunny side -- though I ...

14

The principles of Difference Image Analysis (DIA) or Difference Imaging, which is very common in modern astronomy for finding new transient sources (e.g. asteroids, variable stars, including microlensing events, and supernovae), is simple in principle but complicated by a lot of practical details caused by real-world observations. The basis, which is set ...

12

The two Vega probes comes to mind, ending their implausible sounding mission of slipping balloons into the atmosphere of Venus with a flyby of Halley's comet in 1986. They took a heavy beating flying through the coma, which is the shell of dust and gasses surrounding the comet itself, at the start of the tail. From a navigational point of view, the goal ...

11

There is a lot that the two missions you mentioned--Stardust and Hayabusa--have taught us about sample return. Sample Contamination: Serious measures were taken with Stardust to control for the possibility of sample contamination, but notable problems were still encountered: However, despite these precautions the Stardust spacecraft outgassing was ...

10

The International Cometary Explorer spacecraft passed through the plasma tail of 21P/Giacobini–Zinner in September, 1985, which I think was the first time the human race had engineered such a rendezvous. Many years ago, in my salad days, I did my PhD research on the encounter.

9

Yes No (see update). From ESA's 15 November 2014 update on the Rosetta mission: Pioneering Philae completes main mission before hibernation 15 November 2014 Rosetta’s lander has completed its primary science mission after nearly 57 hours on Comet 67P/Churyumov–Gerasimenko. After being out of communication visibility with the lander since ...

8

Indeed it's extremely difficult to accurately determine the mass of a comet without flying something past it at close range. Even if you assume an average density (which is not particularly safe, as little is yet known about the internal makeup of comets and how that varies from body to body), no earthbound telescopes (including Hubble) were able to resolve ...

8

Rosetta's approach and odd orbit (described well in the question and answer here: Is this really Rosetta's orbit around 67P?) are designed to gather the necessary information needed to achieve a safe orbit and eventually land Philae. The landing site is being selected now: "As many as five possible landing sites will be identified by late August, before ...

8

Taking q = 0.2531011 AU (perihelion radius) and e = 1.1937160 from the latest ephemeris for A/2017 U1, we get a semimajor axis of $$a = \frac{r_p}{1-e} = -1.3065575~\textrm{AU}.$$ Using the definitions of 1 AU and $\mu_{\textrm{Sun}}$ from here, we get the heliocentric velocity at perihelion of v_p = \sqrt{\mu_{\textrm{Sun}}\left(\frac{2}{r_p} - \frac{1}{a}...

8

If there were no forces on an object, then Newton's First Law tells us that a stationary object would remain stationary, and a moving object will keep moving. So a moving comet or asteroid keeps moving. When there is a force on an object, Newton's Second Law essentially tells us that the object will speed up, slow down, and/or change directions. Rockets ...

7

It turns out that scientists thought the same thing very recently. According to this Anatomy of a Comet article at NASA Jet Propulsion Laboratory's website, related to the Rosetta mission, "Scientists used to think that it was solid and firm, but NASA’s Deep Impact mission (2005), in which Rosetta participated, surprised them. They found that the ...

7

Agreed, orbiting can happen at pretty much any scale. To give an idea, 67P/Churyumov–Gerasimenko has an escape velocity of about 1 m/s. (removed reference to ISS experiment because that didn't rely on gravity) A quick experiment: for bodies that weigh 1 kg each and a radius of 1 m, the formula given by @Tildalwave yields an orbital speed on the order of \$...

7

TildalWave's answer is good when only considering the two bodies, but as Pepijn and mart note, for many purposes it is also important to consider the other forces at work, which brings me to one of my favorite learnings about orbital dynamics. In many practical scenarios, we need to consider the influence of the Sun, which exerts tidal forces that become ...

7

The only form of ice that we see naturally in bulk on Earth is Ice I, all within the sub-h variety. There's no place on Earth that gets cold enough for any other form--but that's not necessarily true for the rest of the solar system. Unfortunately for this question, there is nowhere in the solar system that we could ever find any type of ice that depends ...

7

Actually, Ice VII has been discovered in diamonds on Earth. The water is first trapped in the diamond as the latter is formed deep in the mantle. Then when the diamond cools at the surface its rigid lattice retains the high pressure in the interior enabling the water to reach a combination of temperature and pressure where it forms Ice VII. The presence ...

7

TL;DR: It wouldn't work, because you wouldn't be able to keep the comet at L1. The collinear Lagrangian points (L1, L2, and L3) are unstable; if a body were to be placed at one of these points, any perturbation - no matter how small - will move the body away from the point, at which point gravitational and/or centrifugal forces will move the body further ...

7

It is a “Fast Mission” opportunity. These are missions that address an opportunity in the near future that would possibly be missed with the normal mission development timeline. Historically, ESA missions are classified as Large (L), Medium (M) or Small (S). The distinction is not on size of the payload, but on the technology development required for the ...

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(Consider this a spaceholder until I get around to the hard part of the answer) Principally there's no lower size above atom scale. But I would say that for stable orbiting, the gravitational force should be the dominant force compared to solar wind etc. This would depend qualitavly on these factor: Mass of the 'central' body - the heavier the less relative ...

6

I did some research, and according to this source, Philae has only one, upward-pointing, thruster, the "Active Descent System". It has no downward-facing thrusters that could kick up dust. This thruster will likely only be used when Philae is already on the ground to keep it there while it anchors itself, not for course correction. Rosetta contains a ...

6

Assuming that our vaporization is at least as effective as a rocket engine (ISP 500) that gives 2.5m/s delta v Unlikely - the rocket engine uses a shaped engine bell tuned to give the best thrust (put simply) over a several minute burn. Whereas vaporised material from the comet itself would consist mainly of low energy expanding gas and its "exhaust angle" ...

6

I used the JPL Horizons database and downloaded the predicted positions (state vectors) of Earth and Comet 67P at 10 day intervals from 1600-Jan-01 to 2500-Dec-01. edit: As @pericynthion pointed out in comments, since comets are subject to various non-gravitational forces, including "propulsion" by gasses vented unevenly and unpredictably by the rotating (...

6

These are all space probes that have visited or investigated comets throughout history, mostly from the Halley Armarda, a group of probes launched to investigate Halley's Comet during its 1986 approach. Bear in mind the portraits are very stylised so certain identification is kind of difficult. Across the top from left to right: Sakigake/Susei Japan's ...

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