Eros, the first Near Earth Asteroid
Eros is the first Near Earth Asteroid to be discovered, named after the Greek God of Love because of its proximity to the Earth. The asteroid was discovered towards the end of a century of dramatic and unexpected discoveries in the Solar System. Eros became the focus of scientific scrutiny because of how close it got to the Earth.
Eros was discovered on a crisp August night in 1898, when the German astronomer Gustav Witt peered through his telescope at the Berlin Observatory. A faint speck of light was passing through the constellation of Aquarius. The object moved far more rapidly across the night sky compared to the asteroids occupying the main belt between Mars and Jupiter. Witt had stumbled across the first known Near Earth Asteroid (NEA), objects that had been pushed towards the orbit of the Earth by gravitational interactions with the planets in the Solar System. His colleague August Kopff confirmed the discovery, and the two astronomers named it Eros after the Greek God of Love, referring to its close approach to the orbit of Earth.
The complex shape of Eros. (Image Credit: NASA).
At that time, astronomers were still piecing together the architecture of the Solar System. The first asteroid was discovered only in 1801. The asteroid system was only starting to be recognised as a graveyard of planetary leftovers. Some asteroids had never coalesced into a planet, others were the fragments of worlds that were battered to bits by collisions. Eros stood out as an outlier, a wanderer that had drifted far from the crowded lane between Jupiter and Mars. Its orbit, ranging from 1.13 to 1.78 AU brought it to within 22 million kilometres to the Earth. The proximity made Eros an object of scientific interest, a chance to better understand the raw material of planet formation.
The elongated potato
Eros spans 34 kilometres across and is shaped like a peanut or a lumpy potato. Its surface is a mottled gray expanse that bears the scars of being battered by impacts of all sizes. Some of the craters pockmarking the surface are as wide as seven kilometres across. The surface is carpeted by a loose layer of regolith, a fine, coarse dust and gravel that indicates a history of impacts and erosion. Eros is an S-type asteroid, that indicates a stony composition rich in silicates and metals such as iron and magnesium. Meteorites with a similar composition occasionally rain down on the Earth, suggesting that Eros is a fragment of a much larger body that shattered in the infancy of the Solar System.
Eros is an... oddball? (Image Credit: NASA).
Eros has a density that is slightly in excess of the crust of the Earth, indicating a solid structure. However, some scientists believe that it is not a single cohesive mass and is a rubble pile of rocks loosely held together under the influence of gravity. Eros spins on its axis every 5.27 hours, and the rapid twirl causes the days and nights to flicker in a rapid rhythm. The brightness of the asteroid rapidly fluctuates as it tumbles, reflecting light from its pockmarked surface. Eros makes close approaches to both Mars and Earth during its orbit around the Sun.
A window to the past
Eros is a time capsule, preserving the conditions of the Solar System 4.6 billion years ago, when the Sun was just born. It carries hints of the processes by which planets were assembled. Its composition is believed to be similar to the material that coalesced into the inner rocky worlds, Venus, Earth and Mars. Eros belongs to a population of asteroids monitored for potential impactors. The surface holds potential resources, including metals that could fuel space exploration and construction one day. Asteroids such as Eros can be mined, the materials harvested to build habitats beyond the Earth.
The NEAR Shoemaker mission
The proximity of the asteroid made it an attractive target for close-up study. On 17 February 1996, NASA’s Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission was launched by NASA to unravel the mysteries of Eros. The spacecraft was the first in NASA’s Discovery Programme, and the mission marked a bold new step in asteroid exploration. It was the first dedicated mission to study an asteroid from up close. The spacecraft made a gravity assisted flyby of Earth, and briefly gazed at the asteroid 253 Mathilde before arriving at Eros on 14 February, 2000 after a four year journey.
Illustration of NEAR Shoemaker's rendezvous with Eros. (Image Credit: NASA).
Shoemaker mapped the peanut-shaped surface with cameras, spectrometers and a laser rangefinder for nearly a year. The mission confirmed that Eros was a stony asteroid with a thin, dusty crust. On 12 February 2011, a year later, Shoemaker made history by softly landing on the surface of Eros. This was the first spacecraft to touch down on an asteroid. The probe was not even designed to land, but transmitted data from the surface for two weeks, offering an unprecedented view from the ground level. The probe was named after the planetary scientist Eugene Shoemaker. The mission transformed our understanding of Near Earth Objects.