Discovery of Eris and the Reclassification of Pluto

On July 29, 2005, a team of astronomers led by Mike Brown announced the discovery of Eris, a dwarf planet located in the scattered disc region beyond Neptune. This significant astronomical finding played a crucial role in the reclassification of Pluto as a dwarf planet.

Background

Prior to the discovery of Eris, Pluto was considered the ninth planet in our solar system since its discovery in 1930. However, advancements in telescopic technology and a better understanding of the Kuiper Belt—a region of the solar system beyond Neptune filled with small icy bodies—led astronomers to question Pluto’s status as a planet.

Discovery of Eris

• Date of Announcement: July 29, 2005
• Discoverers: Mike Brown, Chad Trujillo, and David Rabinowitz
• Location: Eris was discovered using images taken at the Palomar Observatory in California.
• Characteristics: Eris is slightly smaller in diameter than Pluto but is more massive. It orbits the Sun at a greater distance, taking approximately 557 years to complete one orbit.

Impact on Pluto’s Classification

The discovery of Eris, which was initially thought to be larger than Pluto, sparked a debate within the astronomical community about what constitutes a planet. This debate culminated in the International Astronomical Union (IAU) redefining the criteria for planet classification in 2006.

IAU’s Definition of a Planet (2006)

1. Orbits the Sun: The body must orbit the Sun.
2. Sufficient Mass: It must have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape.
3. Cleared the Neighborhood: It must have cleared the neighborhood around its orbit.

Pluto failed to meet the third criterion, as it shares its orbital zone with other objects in the Kuiper Belt. Consequently, Pluto was reclassified as a “dwarf planet,” a category that also includes Eris, Haumea, Makemake, and Ceres.

Broader Historical Significance

The reclassification of Pluto marked a significant shift in our understanding of the solar system. It highlighted the dynamic and evolving nature of astronomical science and the importance of continuous observation and discovery. The debate and subsequent decision also underscored the need for clear definitions in scientific classification.

The discovery of Eris and the reclassification of Pluto continue to influence the study of planetary science and the exploration of the outer solar system, prompting further research into the characteristics and origins of dwarf planets and other trans-Neptunian objects.