David Rothery

David Rothery

Prof of Planetary Geosciences, Open Univ
Moons Educator
Books:
Moons (2015) OUP
https://www.youtube.com/watch?v=l7FkCOwpCdk
Planet Mercury (2014) Springer
Planets (2010) OUP
http://www.open.ac.uk/people/dar4

Location Milton Keynes

Activity

  • @LindaGilbert "Species that are confined to one planet are ultimately doomed" this is undeniably true. Quite apart from the Sun ultimately swelling up to a red giant, natural (or, much sooner, anthropogenic) climate change is likely to bring down our civilization even if humanity or other kinds of life survive. Don't put all your eggs in one basket. (And, by...

  • For the record, moderators cannot remove posts. Only FutureLearn can do that, for example if a post is reported for breaching community standards (and I am not aware of that having happened during this presentation).

  • I think perhaps the video has been removed because it is not 10 years old. I have emailed the organisers (at the Lunar & Planetary Institute) to ask if the video can be reinstated.

  • Not necessarily, but lunar meteorites that have sampled the sub-surface are clearly akin to what was collected at the surface.

  • If it's frozen already, then it wont boil. Only a very foolish astronaut would try to melt precious lunar ice in a vacuum.

  • Absolutely not. Carry on through the course and you will find out that microbes living mostly on the bottom of internal oceans are the most feasible kind of life.

  • Hadley Rille, where Apollo 15 landed, is a collapsed lava tube. Many others are known.

  • The only moon with a dense atmosphere is Titan, but its whole atmosphere is orange and there are no known storms. Are you thinking of the planet Jupiter?

  • I can't speak for 'most geologists', but as usual in journalism the impact of the study it reports is exaggerated. It remains very widely accepted that very large volume eruptions on the Moon ended before 3 billion years ago. It is accepted that some substantial areas received big lava flows until about 2 billion years ago (proved when a Chinese sample...

  • @BenC you can see the replay already at the original link. The YouTube version will take a few more weeks because captions have to be added and some image rights need to be cleared.

  • Close, but the Cretaceous ended about 66 million years ago.

  • This may be a language issue. Does “split apart” make more sense to you?

  • Radioactivity never 'ceases'. It decreases by 50% for every half-life that has elapsed. Radioactive heating inside a planet, or moon, therefore decreases over time so that volcanic activity becomes rarer and may eventually cease entirely (because the small amount of generated heat can escape in other ways).

  • Not for Apollo. The Space Shuttle had ceramic tiles as a heat shield on its underside, and some of those came loose.

  • What Julian says is true of Ariel, Umbriel, Titania and Oberon - but for all the more recently discovered moons of Uranus from Miranda (a human character in The Tempest) onwards the names are of Shakespearean characters. Ariel, Titania and Oberon happen to be in Shakespeare, whereas Umbriel is a character in Alexander Pope's "The Rape of the Lock", where Ariel...

  • When you click it reveals a larger image with annotation, to help you understand the text in our written answer.

  • That's the quality of the data we have, so we have to work with it if we want to do science.

  • Some for hours, some for months. Most of the plume material falls back onto Io, but some ends up dispersed along Io's orbit.

  • Not at all. Almost all the erupted material ends up on the surface, and is buried by later eruptions whose weight causes subsidence. The rocky (silicate) component of Io has probably been recycled several times in this manner.

  • @LindaGilbert @InekeFioole sorry about that. I've fixed the link now.

  • @IsaacNumoah the moons of other planets all have names. For example, one of Jupiter's moons is named Europa, and other is named Ganymede. Our moon has a name too, which is "the Moon", with a capital-M.

  • I have just tried it, and it works for me. It is an ESA website and should be accessible for everyone, irrespective of location. Possibly the website was offline temporarily. If you still can't see it, try a different browser.

  • @YvonneWilliams be in no doubt that this is a scam. Paid-for names will not be accepted by the IAU, and the website that you linked to is trying to part gullible people from their money.

  • What do you mean by "understand"? Can you understand the rebound effect that causes a single peak in the smaller complex craters? If so, it is just a small step to accepting the evidence or ring-like rebound within larger craters reading to peak rings instead of a central peak.

  • Io

  • @MaryR This is the effect that exaggerates the eccentricity of their orbits, which is why tidal heating is effective.

  • Why would you expect the difference in size between Ganymede and Titan to be visually apparent? Titan's radius is only slightly less than Ganymede's.

  • @MaryR There are a lot of misconceptions to unpick in this thread. Tidal forces on Earth have not changed (well, they are becoming very slightly less over time as the Moon's orbital radius increases). Volcanism has little to do with heat in the Earth's core (it is driven almost entirely by processes in the mantle). There is no current/recent upwards global...

  • @MichaelBath Caroline Herschel was Wm Herschel's sister, and an astronomer in her own right.

  • Short answer: gravity. Long answer: https://www.youtube.com/watch?v=jZUaJZ4FeUI&t=17s

  • @SueC probably, but we will have to wait patiently to see ;-)

  • I hope by now you have reached 2.8 and learned that Galileo did not give names to 'his' 4 moons.

  • @InekeFioole No, you've misunderstood. You need a third body to carry away the excess kinetic energy if you want a free moving body to end up orbiting a planet that is comes close to.
    What we are saying in the final sentence is that present-day Triton could have been one member of a double object (like present-day Pluto-Charon) that was captured by Neptune,...

  • Orbital speed depends on the strength of gravity and distance. A moon in a larger orbit will travel more slowly than a moon in a smaller orbit about a given body.
    Callisto is not small. It is left off because it orbits outside Callisto's orbit and is not relevant because its orbital period is not in resonance with the other three.

  • Yes that's correct. You will learn about this later. The cause is tidal drag.

  • A planet with the enormous mass of Saturn will scarcely feel any effect if a 100 km icy moon becomes smeared out as a ring rather than being in a single ball.

  • There is no formal rule. At least, the International Astronomical Union has not made a rule to cover this.

  • Everything has gravity. The more mass. the more gravity, so you can't base a definition of a moon on whether or not it 'has gravity'. For moons that have never been studied during a close flyby by spacecraft we can't tell if they have a core or not - so possession of a core would be an unsatisfactory definition.
    As you will see later in this course, a 10...

  • In detail, yes - but there are characteristics that many of them share too, as you will see as the course progresses.

  • He doesn't?! Well, at least he has a nose, which means he doesn't smell terrible ;-)

  • @RoyHolton that was one person's unscripted opinion. Make of it what you will.

  • @YvonneWilliams buzz when you think you spot one ;-)

  • @YvonneWilliams I'm sorry if the video is not playing for you. Try again, and then try with a different browser