In April 2011, Makemake – one of five dwarf planets in our Solar System – passed between Earth and a distant star. Using seven telescopes, an international team of astronomers observed the event, known as stellar occultation, and through careful analysis, have determined the planet's size, density, and even the nature of its atmosphere.
Dwarf planets are celestial bodies that directly orbit the sun, but do not possess the gravitational forces necessary to clear their orbits of other astronomical objects. Makemake shares our Solar System with four other dwarf planets; Ceres, Eris, Haumea and Pluto. Easily the most famous of the diminutive planets, Pluto was controversially downgraded to dwarf status in 2006.
Makemake's orbit lies towards the very edge of the Solar System, residing beyond icy Pluto but closer to the sun than Eris. Its study was an international effort, led by Jose Luis Ortiz of the Andalucian Institute of Astrophysics in Spain. A total of seven telescopes across Chile and Brazil carefully watched the small planet as it crossed the path of distant star Nomad 1181-0235723, closely observing the change in light. The entire event lasted just one minute.
Prior to the study, it was thought possible that Makemake would have an atmosphere similar to that of Pluto. However, as the small celestial body passed in front of the distant star, the light disappeared and reappeared abruptly, rather than slowly fading and brightening. This strongly indicates that Makemake has no significant atmosphere.
Though the dwarf was already known to be some two-thirds the size of Pluto, the study has allowed the team to confirm that it is approximately 1,430 km (889 miles) across in one direction and 1,500 km (932 miles) the other, making it not quite spherical. The planet's overall density was found to be around one-third of Earth, at 1.7 grams (.06 oz) per cubic centimeter.
The path of the shadow of Makemake on April 23rd, 2011 (Image: ESO/L. Calçada/Nick Risinger (skysurvey.org))
Dr. Ortiz commented on the significance of the findings, stating that “Our new observations have greatly improved our knowledge of one of the biggest [dwarf planets], Makemake – we will be able to use this information as we explore the intriguing objects in this region of space further.”
Previous studies have been carried out on the other four dwarf planets in the Solar System. Ceres is the only dwarf planet that resides within the inner Solar System, making it the only one of the five to have been analyzed directly by telescopes. Eris and Haumea have been previously analyzed using the same occultation method as used on Makemake. Both studies yielded interesting results, with Haumea found to be icy like Pluto, while Eris was discovered to be the largest of the five small planets.
The study of Makemake is just the latest of a great many studies carried out by the European Southern Observatory (ESO). Recently, the Very Large Telescope and Canada-France-Hawaii Telescope were able to identify the first ever “rogue planet”. The planet, which is not thought to be gravitationally bound to any star, resides some 100 light-years from our own Solar System.