I recently came across this youtube video, in which a few people are singing about the history of exoplanet discovery.

It suggests that, in the 1990s, exoplanet hunters were largely ignored or ridiculed. Is there any truth to this?

  • $\begingroup$ In the press release about Trappist-1, one of the scientists said that her superiors dismissed it as "stamp collection" because we'd never actually be able to examine the exoplanets more closely. $\endgroup$ – Phiteros Mar 11 '17 at 7:02
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    $\begingroup$ You should read about Bill Borucki, the guy who championed the creation of the Kepler spacecraft (which has since found thousands of exoplanets). It took him decades of proposals and research to convince NASA that something like Kepler was actually worth the money. He was trying to get Kepler funded way back in the 80s. $\endgroup$ – zephyr Mar 13 '17 at 13:26

Everyone expected exoplanets to exist - there was no reason to suppose that the conditions that existed when the sun formed were unique, and we knew that multiple star systems were common. Newton wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design"

Observations in the 80s were not ignored, they just lacked sufficient evidence. I.e, they were considered and properly rejected. Better observations have since confirmed some of the planets that were "discovered" in the 80s, but denied others. Scientific scepticism means that you don't accept something without evidence.

We knew that finding planets would be hard. The technology of sensitive ccd devices that could be used for constant monitoring of multiple stars didn't exist in a form that could be put on a space telescope, and there were other priorities for space science: solar system exploration.

Knowing that planets would be impossible to observe with contempory technology meant that "planet hunting" wasn't a thing. The first planet to be detected was around a pulsar, as the detection depends on changes in the timing of the pulsar, not on measurements of variations in light intensity during a transit, or doppler shift as the star is wobbled.

  • $\begingroup$ Have you got any evidence to support some of the claims here? Which planets were discovered in the 80s? $\endgroup$ – ProfRob Mar 12 '17 at 23:35
  • $\begingroup$ Well, for example Gamma Cephei Ab, First suggested by Campbell et al, 1988, claim withdrawn in 1992. Planet confirmed to exist in 2002. $\endgroup$ – James K Mar 13 '17 at 18:19
  • $\begingroup$ Agreed, that's a good example of where the data were not quite good enough in the 80s, but clearly there was activity in that direction. Nobody was being ignored or ridiculed that's for sure. $\endgroup$ – ProfRob Mar 13 '17 at 18:47

The problem in the 80s and 90s for exoplanet hunters was that nobody expected that they would be able to detect any planets, even if they were there.

When I was a postgraduate/postdoc at Birmingham University in the early 1990s, there was a solar and stellar seismology group that used a Potassium magneto-optical filter that achieved radial velocity precisions of some 10s of m/s. From the introduction of Innis et al. (1991).

On much longer time-scales, accurate velocity measurements of a star to the 1-m s-1 level will allow a search to be made for possible planetary companions. For example, the reflex motion of the Sun, due to the orbit of Jupiter, has a semi amplitude of around 12.5 ms"1 , with aperiod of 12 yr. A very long series of observations (decades to centuries) could reveal the presence of similar motions of solar-like stars. A further paper (in preparation) will discuss the long-term (‘planetary search’) aspects of the velocity measurements of this star."

This paragraph illustrates that the potential and the ideas were there, but it also illustrates why it was difficult to get funding and access to telescopes to pursue these ideas.

The expected timescales for these small variations in radial velocities were years and decades and the expected signals were about at the limits of the precisions of the instruments at hand. Other astronomers were not convinced that such absolute accuracy could be maintained over such long durations.

What changed everything was the discovery of "hot Jupiters" in orbits of only a few days and which caused radial velocity variations that were bigger than the precisions that spectrographs were capable of - especially the newly developed iodine cells (see Marcy & Butler 1992).

So, I do not think it is the case that exoplanet hunters were "ignored and ridiculed", it is simply that planetary formation scenarios did not permit the formation of "hot Jupiters" and thus nobody expected that planets could be detected with the available technology without observing stars for years, if not decades. It thus required time on telescopes that was dedicated to this purpose.

As it turns out, and with the benefit of hindsight, anyone with a CCD camera and a modest sized telescope can identify the transits of hot Jupiters. But even if someone had gone out on a limb and searched for such a thing systematically, they would have been unable to confirm their discovery (as opposed to the vast numbers of possible false positive transit signals) without spectroscopic backup to confirm the planetary mass of the companion. The first transiting planet was found by searching for transits among hot Jupiters identified by the doppler method.


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