Astroblog

Pluto as seen from Nix

The current passion for astronomical doomsday, as exemplified by unwarranted concern about comet C/2010 X1 Elenin and the mythical planet Nibiru, is sad, given the wealth of real, interesting but non-threatening astronomical events happening. However, we can use this interest as a “teachable moment” to give people a better understanding of the sky and the people who watch it.

I was recently forwarded an email from someone who was puzzled as to why amateur astronomers had not detected Nibiru, and what he could do to search for himself. Firstly, how do you go about finding an unknown object?

At this very moment, hundreds of amateur astronomers are scanning the sky looking for a glimpse of an as-yet undiscovered comet or asteroid (as well as the supernova hunters). Similarly, robotic telescopes such as LINEAR are also scanning the sky, looking for asteroids that have the potential to come threateningly close to Earth.

By definition, we don’t know where these objects are, but we can make educated guesses. Asteroids are mostly found in roughly the same plane as Earths’ orbit, so asteroid surveys tend to be around the ecliptic. Comets can come from any direction in the sky, so we have to cover most of the sky when looking for them. Generally, most amateurs work systematically, regularly observing a broad swath of sky repeatedly over a number of days. In these days of CCD cameras, multiple wide field images are taken, and the images inspected for points of light that move between successive exposures. Then comes the task of deciding if these moving points are instrument glitches, a known object, or a real discovery.

Pluto imaged by myself with the Global-rent-a-scope GRAS05 instrument, a typical serious amateur instrument.

What are the limits of the objects that amateurs can detect? With modern CCD cameras and instruments, a reasonably well equipped amateur can see objects between magnitude 14 (how bright Pluto is at the moment) and magnitude 18 (the discovery magnitude of some recent comets). So what sort of objects could amateurs be expected to detect? Quite small faint ones; for example, if Earth was at the distance of Pluto, it would be around magnitude 12, readily visible by the majority of amateur comet hunters.

So what about Nibiru? What do we know of its properties? Well, it is claimed to have an orbit which takes 3600 years to complete. At the moment, it is claimed to be close to the Earths’ orbit around November/December 2012 (there have been other dates, Nibiru was originally predicted to turn up in 2003). From Kepler’s laws we can calculate that the diameter of the orbit must be 496 astronomical Units (AU, the distance of Erath to the Sun http://www.2012hoax.org/nibiru) (see also here http://arxiv.org/abs/1009.1374) compare this with Pluto’s orbit of 39.6 AU. From this we can also work out its orbital velocity (http://www.sjsu.edu/faculty/watkins/orbital.htm) which turns out to be 3.8 x 10⁸ Kilometres per year (or roughly 2.5 AU a year). Working backwards, we find that right now, today, Nibiru should be about 4.2 AU away, closer to us than Jupiter is. How bright would such an object be?

It depends on the size of the object and how reflective it is. The Moon isn’t very reflective, its surface is quite dark, but it is very bright because it is close to us. There is a formula to work out how bright any given object is (http://space.wikia.com/wiki/Absolute_magnitude). The formula is a little messy, depending on the angle of illumination of the object, but any object outside Earths’ orbit will be at least 2/3 illuminated. If we assume that the object is the size of Earth, and is as reflective as Pluto (a good assumption for an object allegedly coming from the outer solar system), then it will have a magnitude of around 4, faint but easily visible to the unaided eye in all but the most light polluted skies. At the very least the supernova hunters would have noticed it, let alone the comet and asteroid hunters, months ago. If it was at the orbit of Saturn, about a year ago, then it would be around magnitude 6, easily visible in binoculars.

That is for an Earth-sized object, but Nibiru is claimed to be larger. The size given for Nibiru is varied, but usually runs from Jupiter sized, to many multiples of Jupiter’s size (from Brown Dwarf stars to Red Dwarfs). A Jupiter sized planet at the calculated current distance of Nibiru would have a magnitude of -1 to -2. That is it would be outshining most stars and really, really obvious.

Is there a way for Nibiru to remain invisible? One person maintains that Nibiru is already in the inner solar system, just inside the orbit of Venus only 69 x 10⁶ kilometres away. It is not visible because it is too close to the Sun. However, to have crossed the inner solar system in the first place it would be highly visible. The only way it could be hidden is to have a highly unlikely orbit, where Nibiru precisely tracks Earths orbit around the Sun, from when Nibiru is magnitude 12. This is amazingly, astoundingly unlikely.

But that only hides it incompletely from Earth. As people know, I spend a lot of time looking for Venus in the daylight. An Earth sized object would be visible in daylight to a reasonable distance from the Sun (just like Venus). A Jupiter sized object just inside Venus’s orbit would be magnitude -10. It would be a crescent phase, but still very bright and easily visible in daylight even quite close to the Sun, as well as readily visible just after Sunset. Even if Nibiru was as black as coal it would be bright from the reflected light of the Sun.

Nibiru can't hide from the STEREO satellites.

And let’s not forget the satellites, the STEREO and SOHO instruments are watching the Sun from different angles to Earth, an Earth sized object would be painfully obvious in either of the STEREO instruments (either ahead or behind), as well as the SOHO instruments.

The dedicated bands of comet hunters who peruse the raw STEREO and SOHO images looking for comets would notice something immediately.

So an Earth-sized, unknown astronomical object would be picked up by the amateur astronomical community in the outer solar system, any such an object would be visible to the unaided eye by the time it reached Jupiter’s orbit. Anything of Jupiter sized or bigger would be painfully obvious by the time it reached Jupiter’s orbit. It couldn’t be hidden by anybody.

You yourself can go out this afternoon or evening and confirm that there is no Nibiru, using just your eyes.

Nibiru and Google Sky (http://bbs.keyhole.com/ubb/ubbthreads.php?ubb=showflat&Number=1360179&page=all)

Labels: Astronomy, Pseudoscience, science communicators