Comets and As­ter­oids

433 Eros is a large near-Earth ob­ject which may one day get very up close and per­sonal

Sky at Night Magazine - - CONTENTS -

Mi­nor planet 433 Eros is a siliceous or S-type as­ter­oid, which means it has a stony com­po­si­tion. At 34.4x11.2x11.2km its elon­gated body is the sec­ond largest near-Earth ob­ject known. It be­longs to a group of ob­jects called the Amor as­ter­oids, named after 1221 Amor. All the as­ter­oids in this fam­ily have or­bits that re­main out­side Earth’s or­bit.

Eros was the first as­ter­oid to be or­bited and landed on by a space­craft. The craft in ques­tion was NEAR Shoe­maker, which en­tered its or­bit in 2000 and soft landed the fol­low­ing year.

Like most Amor as­ter­oids, Eros’s or­bit crosses Mars’s. At aphe­lion it is 1.78 AU from the Sun and at per­i­he­lion comes as close as 1.13 AU. At favourable op­po­si­tions – which oc­cur every 81 years – Eros can ap­pear as bright as mag. +7.0. This year, though, when Eros reaches op­po­si­tion on 7 De­cem­ber, it will ap­pear as a mag. +9.7 ob­ject in the ill-de­fined con­stel­la­tion of Camelopardalis. Its dis­tance from Earth will be about 40.5 mil­lion km, which may sound close but is sig­nif­i­cantly fur­ther than our 26.7 mil­lion km close en­counter with it on 31 Jan­uary 2012.

It’s thought that grav­i­ta­tional per­tur­ba­tions could al­ter Eros’s or­bit from a Mars-crosser to an Earth-crosser within a cou­ple of mil­lion years. Eros is classed as a po­ten­tial Earth im­pactor; wor­ry­ingly it is five times the size of the as­ter­oid that caused the ex­tinc­tion of the di­nosaurs.

At the start of De­cem­ber, 433 Eros is lo­cated 2.5° east of the east­ern end of the as­ter­ism Kem­ble’s Cascade in Camelopardalis. It then arcs west as it heads south. Its dis­tance from Earth con­tin­ues to de­crease dur­ing De­cem­ber, and so its ap­par­ent bright­ness in­creases. On 1 De­cem­ber, when Eros is 2.9 AU from Earth, it shines at mag. +9.9. By the end of the month its dis­tance will drop to 2.2 AU and its mag­ni­tude will rise to +9.2.

Cur­rently 433 Eros never passes be­tween Earth and the Sun, but that may change

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