Searching for Other Earths

This morning I’m teaching a third-year class on the topic of extrasolar planets. Its part of a module called Life in the Universe which we’ve run since 1998. It was one of the first courses, perhaps THE first course, in astrobiology in Europe and was widely reported in the world’s press (BBC ).

We’ve only been discovering these planets in orbit around stars other than the Sun since 1995, but in some senses there has been an expectation of their existence going way back to Copernicus . Though Copernicus was not the first to propose a Sun-centred planetary system (that privilege goes to Aristarchus ) it was his rejuvenation of heliocentrism, as its called, in the C16th that led to Giordano Bruno declaring “Innumerable suns exist; innumerable Earths revolve about these suns … Living beings inhabit these worlds.”

I guess Copernicanism can be summed up in the telling phrase “if the Earth is a planet, then the planets may be Earths; if the Earth is not central, then neither is humanity”.

So we’ve been looking since 1543 basically, and in 1995 we began to find those elusive extrasolar planets. How long before we happen to chance upon another Earth? Maybe in our lifetime. Now that’s a great topic for discussion!



    January 13, 2005

    By some strange coincidence I caught the last 10-15 mins of a
    programme on Radio 4 last night, about just this subject. The
    things I remember where

    * the student astronomer in the UK who became the first
    amateur to be involved in discovering planets since “Herschel”:

    * That astronomers are puzzled about whether our planetary
    configuration is strange or the ones they are discovering. The
    relationships of these planets to their respective suns seems to
    be counter to some of the accepted theory.

    * There are some strange orbits in other systems

    What did strike me though, was that science programmes on
    Radio 4 are great, because they lead you through subjects, often
    providing a human element to sometimes difficult subjects.

    The device of the presenter undertaking the journey of discovery
    on your behalf seems to work really well.


    January 13, 2005

    The discussion over planetary configuration in these recently discovered systems is an interesting one. Picking up on mearso’s point – scientists do not have the technology capable of resolving these orbiting bodies. It is the theoretician who uses the ‘wobble’ of the star (induced by the gravitational presence of an orbiting body) to calculate the distance and lower limit for the mass of that object. This gives no indication of whether the body is another star in part of a binary system or a planet. Some of these systems contain a body in very close proximity to the sun-like star. The question of how such a massive body (between 0.5 and 3.5 times the mass of Jupiter – managed to form so close to the star is intriging. It seems to go against the grain of the model scientists currently use to explain the formation of our solar system – the solar nebula hypothesis. Even if one assumes that this body is a planet and has traversed inwards from its appropriate orbit according to the solar nebula hypothesis towards its parent star problems still persist.

    Another issue is that the current methods of detection bias the type of planets found. Only planets of considerable size (comparable with Jupiter) will have the required gravitational influence on the parent star to induce a ‘wobble’ of significant magnitude that can be measured from Earth. I would imagine that with such a massive body this close to the star that a terrestrial type planet would have a difficult job coalescing and sustaining a suitably stable orbit within the habitable zone for a sun-sized star in such a system. But as mentioned earlier, our results are significantly bias towards these ‘odd’ orbiting systems. There is nothing to say with the right technology that other stars yet to yield results might not be harbouring a ‘wannabe’ Earth. That is the debate as I understand it!


    January 13, 2005

    Yes, journeys of discovery DO work well!

    I was once unfortunate enough to turn up at a production
    planning meeting for a science communication TV series. The
    serious suggestion for this series of programmes was a sort of
    Supermarket Science idea. Dale Winton would appear on roller
    skates (I’m not joking) trundle to the nearest aisle, and
    appropriate some everyday object or produce. On his return to
    the checkout the assembled boffins would tell us something
    “fascinating” that we (didn’t) want to know about the science of
    the appropriated object.

    Talk about dumbing down! Seems to me they think the great
    unwashed have limited attention spans and aren’t able to engage
    in journeys of discovery.

    In fact, I was guilty of derailing the meeting and proposed a
    series of programmes that did something similar to our courses
    at “CASE”: . Great
    and grand narratives about the history and evolution of science,
    basically. Life, the Universe and Everything, if you like. I was
    temporarily successful in raising the bar for the producers who
    became interested in the personal journey approach.

    Sadly, nothing came of the plans. But the entire affair spoke
    very strongly to me on the question of science communication.
    They make judgements all the time on the level of public
    understanding, often misjudging or underestimating public
    interest and expertise.


    January 13, 2005

    I was thinking last night, that global scientific phenomena are
    often covered, like last nights Horizon on global dimming, but
    more everyday ‘local’ science is often left out. I think Adam Hart-
    Davies’ programmes are great fun. It seems that TV has no
    equivalent to the New Scientist mag.

    Maybe its just me but I’m often fascinated by the stories behind
    the science. I found a great bookin the charity shop – A time-life
    book called The elements. The thing I liked were the photos of
    each of the elements (well, the photogenic ones) and a little
    piece about each. For example Tungsten comes from the
    Swedish meaning strong stone.

    Mark Brake

    January 13, 2005

    Take a look at the flashest
    “Periodic Table”: on the web!

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