Mercury in motion

If you missed yesterday’s rare Mercury transit across the Sun – the last was in 2006, the next in 2019 – then where were you! [Busy… – Ed]  But even if you were paying attention you’re unlikely to have had as wondrous a view as that of Nasa’s Solar Dynamics Observatory.

Mercury Transit 2016 via SDO

They’ve helpfully released a stunning time-lapse video compressing the entire 7 hour spectacle into a digestible couple of minutes.  I recommend switching to full screen mode and cranking up the volume.  Enjoy!  [Video credit: NASA’s Goddard Space Flight Center/Genna Duberstein. Music: Encompass by Mark Petrie]

And from the BBC report

Open University’s Prof David Rothery said the celestial event did not present any novel scientific opportunities – but was special nonetheless.

“From this transit, we’re unlikely to learn anything we don’t already know,” he told BBC Inside Science. “But what a wonderful event for showing people Mercury. It’s a hard planet to see.

“Historically, transits were of immense importance.”

In the 1700s, for example, it was observations of Mercury and Venus slipping across the Sun that allowed astronomers, led by Edmund Halley, to pin down the dimensions of the known Solar System.

Prof Rothery is a Mercury expert and a leading scientist on the European Space Agency’sBepiColombo mission to the diminutive planet, which will launch in 2017 or 2018.

Mercury has already been visited by two Nasa probes: Mariner 10 flew past in 1974 and 1975 and Messenger spent four years in orbit until its planned crash landing in 2015.

“[Messenger] told us an awful lot. It really told us we don’t understand Mercury – because there’s a lot of things which just don’t stack up,” Prof Rothery said.

“It’s an airless body, with lots of craters… But there’s been a long history of volcanic activity, fault activity – and the composition, that began to be revealed by Messenger, is weird.

“There’s very little iron at the surface but it must have a ginormous iron core, because it generates a magnetic field – which Venus, Mars and the Moon don’t.”

Current speculation suggests that Mercury experienced a glancing collision with Venus during the early solar system, sloughing off much of its surface in the process – leaving Mercury with a thinner mantle than expected and Venus with a thicker one.

Here’s a post from 2011 which has some details of Messenger’s findings.

  • the rich get richer

    Good video and it should make an observer think of the bigger picture and how unimportant one actually is.

  • Korhomme

    Aren’t exoplanets found by observing transits across their sun and the resulting reduction in the star’s brilliance? Yet seeing this tiny speck moving across the sun makes me a bit puzzled; how can something so small reduce the sun’s light enough for us to be able to measure it?

  • Devil Eire

    The frontier of astronomy is all about measuring tiny signals in the presence of noise and the detectability of these signals just depends on how large they are compared to the sources of error (the “signal-to-noise ratio”). For planetary transits, the “signal” is the reduction in brightness during transit and this is proportional to the ratio of the planetary and stellar areas. For Jupiter orbiting the Sun, this is around 1%; for Earth, around 0.01%. So the size of the signal is boosted for large planets transiting small stars. An instrument’s ability to detect this reduction depends on experiment design, a thorough understanding of all the sources of noise and on other factors like the stability of the star’s brightness. It helps that a planetary transit will be periodic, so assuming you can correct for any non-random (systematic) effects, you can average many of these periodic measurements together to improve the precision of the overall measurement and detect these very small dips in brightness.

  • Korhomme

    Thanks; I get the principle, I’m still amazed that it can be done. I see that Kepler has discovered another 1200 exoplanets, and that the measurements must be observed three times to be accepted.

    How small a variation in brightness is measurable? I really can’t imagine that a Mercury-sized exoplanet would be seen above the noise. Is a Jupiter big enough? And aren’t they searching the ‘cinderella’ zone for earth-like planets; so is 0.01% observable?

  • Devil Eire

    How small a variation in brightness is measurable?

    As I said, it depends on the relative size of the signal to the noise, which depends on lots of factors. To detect the smallest planets with Kepler, the planets need to transit a bright star with low variability in a tight orbit.

    I really can’t imagine that a Mercury-sized exoplanet would be seen above the noise.

    Kepler-37b, with a size similar to Earth’s Moon, was detected because it fulfilled these requirements, even though the dip in brightness was only 0.00161%.

  • Korhomme

    Devil Eire has already answered your questions, so there should be no need to be puzzled anymore. Amazed is fine, btw.

    Here’s the Kepler mission website.

    And the details of Kepler-37b – “A sub-Mercury-sized exoplanet in a three planet system orbiting Kepler-37”.

    With the Feb 2013 press release from Nasa.

    The planets are located in a system called Kepler-37, about 210 light-years from Earth in the constellation Lyra. The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. It is smaller than Mercury, which made its detection a challenge.

    The moon-size planet and its two companion planets were found by scientists with NASA’s Kepler mission to find Earth-sized planets in or near the “habitable zone,” the region in a planetary system where liquid water might exist on the surface of an orbiting planet. However, while the star in Kepler-37 may be similar to our sun, the system appears quite unlike the solar system in which we live.

    Astronomers think Kepler-37b does not have an atmosphere and cannot support life as we know it. The tiny planet almost certainly is rocky in composition. Kepler-37c, the closer neighboring planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the farther planet, is twice the size of Earth.

    The first exoplanets found to orbit a normal star were giants. As technologies have advanced, smaller and smaller planets have been found, and Kepler has shown even Earth-size exoplanets are common.

    “Even Kepler can only detect such a tiny world around the brightest stars it observes,” said Jack Lissauer, a planetary scientist at NASA’s Ames Research Center in Moffett Field, Calif. “The fact we’ve discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data.”

    Even with the newly confirmed 1,284 exoplanets, I think it’s still the smallest to date.

    Telescopes, eh?

  • Korhomme


  • Korhomme

    Thanks! I’m very impressed by the precision of the measurements and the telescopes, far far more than I’d realised.

    And now, rather than our solar system and Earth being unique, the thinking seems to be that all stars are likely to have planets; and thus it’s very likely that there are other planets that are habitable, and might well be.

  • Devil Eire

    I’m very impressed by the precision of the measurements and the telescopes, far far more than I’d realized.

    If you thought that was impressive, consider the heroic efforts of the Laser Interferometer Gravitational-wave Observatory (LIGO) team. Their recent detection of gravitational waves involved a detection of mechanical strain (i.e. a change in length divided by the original length) of order 10^-21 . This historic achievement was the result of i) identifying all the possible sources of measurement error and ii) doggedly pursuing a visionary, decades-long campaign of systematically attacking and mitigating each one of these sources.