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Mar 04 2010

Did Spanish Astronomers Steal A Dwarf Planet?

In 2005, a controversy erupted in the world of astronomy over who should be credited with the discovery of a distant dwarf planet then known by the temporary name 2003 EL61. The object in question is located in the Kuiper Belt, a doughnut-shaped icy region of the solar system that lies beyond Neptune. It is classified as a “dwarf planet” — which, counter-intuitively, is not actually a planet. According to the International Astronomical Union (IAU), the official naming body in astronomy, a planet must

(a) orbit the Sun,

(b) be massive enough to have a spherical shape,

(c) be massive enough to dominate its region of the solar system, and

(d) not be a moon.

Dwarf planets are almost planets but not quite – they satisfy criteria (a) and (b), but not (c). There are four other objects officially classified as dwarf planets (although many more may qualify): Ceres, the largest object in the asteroid belt between Mars and Jupiter; Pluto, a large Kuiper Belt Object (KBO); Makemake, another large KBO; and Eris, a large object in the region beyond the main Kuiper Belt, the scattered disk.

Pluto has been known for decades and Ceres for centuries, but Eris and Makemake are much more recent finds, discovered in 2005 by a group of astronomers led by Mike Brown at the Department of Geological and Planetary Sciences at Caltech. As for 2003 EL61, not only has Brown’s team claimed its discovery, but so has a rival team led by Jose-Luis Ortiz of the Andalusian Astrophysics Institute in Granada, Spain.

For a decade, Brown surveyed the sky for distant solar system bodies, using the Samuel Oschin Telescope at Palomar Observatory (the search began in 1998 and finally came to an end in 2008). His colleague Chad Trujillo programmed the telescope to look at a small patch of the sky each night and take a series of three images to single out any objects that moved relative to the background stars. Then a computer would sift through the images and pick out anything that did move, and in the morning Brown would view the interesting images in his office in Pasadena, California. When he found a distant object (the slower an object moves, the further away it must be), he and two colleagues (David Rabinowitz and Chad Trujillo) would study it in detail. Brown and his colleagues benefited from advances in technology: rather than the old-fashioned photographic plates that Clyde Tombaugh used to discover Pluto, they used a modern CCD (charge-coupled device) camera which is ten times more sensitive. Because they didn’t know in advance where to look to find an interesting object, they systematically surveyed the entire section of sky that could be seen from Palomar. Unusually, their survey had no name, though Brown jokingly referred to it as “Three Guys at a Telescope (TGT)”.

Brown and his colleagues already had a track record of interesting discoveries, with objects such as Quaoar, Orcus, and Sedna under their belts. Sedna was more distant than any other trans-Neptunian object then known, but was discovered at the closest point of its 11,214-year orbit, 11 billion kilometres from the Sun, far beyond the main Kuiper Belt. This prompted the team of astronomers to go over all their old images looking for slower-moving objects. It paid off in December 2004 when they found 2003 EL61 on one of those images. They intended to announce their discovery at a conference in September 2005, along with their two other big catches Eris and Makemake, to give them time to study the objects in detail and prepare the relevant scientific papers.

But Ortiz’s team made their move first. On 27 July, they announced to the IAU Minor Planet Center that two days before, Pablo Santos-Sanz had discovered a large KBO on images they had taken two years previously. Brown realised at once that it was the same object his group had been studying for months. He accepted defeat gracefully, knowing that priority for scientific discoveries is determined by who is first to publish, and sent an email to Ortiz congratulating him on his discovery. However, some within the Minor Planet Center were suspicious. Ortiz and Santos-Sanz were relatively unknown, and their “discovery” of 2003 EL61 on two-year-old images came less than a week after Brown’s team had published an abstract using the codename “K40506A”.

At first, Brown naively waved those suspicions aside. Then, on the evening of 28 July, he discovered that a quick Google search for “K40506A” turned up unintentionally public observation logs kept by the Small and Moderate Aperture Research Telescope System (SMARTS), which they had used to track the object. Anyone with an internet connection, a knowledge of orbital dynamics, and a telescope could have located the object and claimed the discovery as their own.

Even worse for Brown’s team, the SMARTS website also contained logs of their observations of Eris and Makemake. They realised anybody who accessed the logs would be able to “discover” these objects too. Due to this unfortunate security risk, Brown was forced to flout normal scientific protocol and announce these two other discoveries prematurely. On 29 July, he notified the Minor Planet Center and called a press conference, announcing that he had discovered the “tenth planet” (but that’s another story).

Brown explained to the media about the observation logs, and before long a major controversy was raging in the minor planet community. Brown was careful to emphasise that he had no solid evidence of dishonesty on the part of the Spanish team. Ortiz and Santos-Sanz would neither confirm nor deny that they had consulted the American team’s observation logs. Then, a SMARTS administrator ascertained that the logs had indeed been accessed by a computer used by the rival team of astronomers — the same computer they later used to email the news of their discovery to the Minor Planet Center. This computer visited the logs several times on 26 and 28 July, each time going straight to the page describing observations of K40506A.

Brown emailed the Andalusian Astrophysics Institute demanding an explanation. Ortiz replied a month later, continuing to evade the question of whether they had indeed accessed the SMARTS records. Instead, he accused Brown of harming science by not immediately announcing his discoveries. Brown responded that he was simply following standard scientific procedure:

Scientists make discoveries, they verify their discoveries, they carefully document their discoveries, and they submit papers to scientific journals. What they don’t do is make discoveries and immediately hold press conferences to announce them […] Our intent in all cases is to go from discovery to announcement in under nine months. We think that is a pretty fast pace.

Ortiz repeated the same criticism in a letter published in the Minor Planet Mailing List, where he finally admitted having looked at the SMARTS archive. However, he claimed, 2003 EL61 had already been discovered by Santos-Sanz the day before, and they had only checked Brown’s logs to confirm that both groups had discovered the same object. If the observing records were on a publicly accessible website (analogous to books in a library), was it unethical to look at them? Mike Brown’s view on this question of scientific ethics was unequivocal:

Any information used from another source must be acknowledged and cited. One is not allowed to go to a library, find out about a discovery in a book, and then claim that discovery as your own with no mention of having read it in a book. One is not even allowed to first make a discovery and then go to the library and realise that someone else independently made the same discovery and then not acknowledge what you learned in the library.

Depending on which Ortiz and his colleagues did, said Brown, their failure to mention the Caltech observations could be considered scientific dishonesty or even fraud. On 14 August 2005, he filed a complaint with the IAU, but no official investigation was ever launched. While the IAU takes no official position, public statements made by Brian Marsden, head of the Minor Planet Center, suggest that he sympathises with Brown for not wanting to announce discoveries prematurely.

During those nine months from discovery to announcement, Brown and his colleagues study an object in detail, so that when they announce the discovery they have some good science to tell to the scientific community and a detailed story to tell to the public. Instead of simply saying “there is a big object out there”, which was all that Ortiz’s team knew about 2003 EL61 when they announced it, Brown’s team are able to make much more detailed announcements.

At the time of Ortiz’s announcement, Brown, Trujillo, and Rabinowitz already knew that 2003 EL61 had a small moon (it is now known to have two), which had allowed them to determine its mass, about 31% of Pluto’s. 2003 EL61 averages 6.5 billion kilometres from the Sun, and its orbit is tilted by 28° relative to the ecliptic. It is about 1,265 kilometres across, and rotates faster than any other known KBO (its day lasts a mere four hours); this rapid rotation causes it to have an elongated shape which is often likened to a football. Brown and his colleagues have deduced from 2003 EL61’s rotation that it has a density of up to 3.3g/cm3. This suggests that it is made almost entirely of rock, but we know from its spectrum that its surface is pure ice. Apparently, 2003 EL61 is a large rocky body with a thin crust of ice, a structure that Brown has compared to that of an M&M. Its moons, on the other hand, appear to be icy.

Brown and his fellow astronomers think all these oddities can be explained by an ancient collision with another large KBO. According to this hypothesis, 2003 EL61 started out billions of years ago as a body similar to today’s Pluto, a large ball of half-ice and half-rock. The force of the impact stripped away most of the outer layer of ice, leaving a core of mostly rock. The angle of the impact was such that it caused 2003 EL61’s rotation to go into overdrive, which in turn elongated it into its unusual shape. Some of the debris blasted off the surface became 2003 EL61’s moons.

This hypothesis is supported by the later discovery that several other relatively large KBOs (ranging from 200-900 kilometres in diameter) appear to have originated from 2003 EL61 in the same manner. Unlike most KBOs, which have more complex surfaces, these objects all have surfaces composed of almost pure ice like 2003 EL61’s moons. What’s more, they are all in very similar orbits to 2003 EL61, forming a “family” of about ten known objects. There are many such collisional families in the asteroid belt, but this is the first known case in the Kuiper Belt. Interestingly, the impact that created all these bodies is believed to have occurred near a region of space where orbits are unstable because of interactions with Neptune; so many chunks of the debris would have been ejected from the solar system or flung inwards into the inner solar system to become comets. 2003 EL61 itself is in an unstable orbit and may become a comet sometime in the next billion years or so.

For three years, 2003 EL61 remained unnamed because it was unclear which group of astronomers should get the discovery credit and hence naming rights. In 2006, Brown’s group submitted a name for 2003 EL61: Haumea, after the goddess of childbirth in Hawaiian mythology. (Brown also wanted to name the two satellites Hi’iaka and Namaka after two of Haumea’s children, who were supposed to have sprung from parts of her body.) Ortiz’s group also submitted a name: Ataecina, after an underworld goddess associated with the Greek goddess Persephone. Although in September 2008 the IAU finally approved the name Haumea, as proposed by Brown, their press release was vague about who should be considered the discoverer. Brian Marsden, told New Scientist that this was done deliberately to avoid an international incident.

So which group of astronomers do get the discovery credit? Unfortunately, the IAU has no protocol for resolving a dispute such as this one. The controversy has dragged on for nearly five years now, and it may be that it will never be resolved.

1 ping

  1. AlunSalt » How I Killed Pluto and Why It Had It Coming by Mike Brown

    […] also tackles the controversy over the discovery of Haumea. At the time I got the vague impression that a slow team of astronomers had missed a planet in […]

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