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Picture of the Day · NASA
Pathfinder on Mars
2026-07-04
On July 4th, 1997, using its own array of fireworks, a parachute, and a cocoon of airbags, the Mars Pathfinder spacecraft bounced like a giant beach ball at least 15 times before it came to rest on the surface of Mars at 10:07 AM Pacific Daylight Time. After its then novel airbag-assisted landing sequence was completed, Pathfinder transmitted this color mosaic to mission operators on Earth. In the scene from another world, the Mars Sojourner robot rover is visible in the foreground, crouched on top of the unfolded Pathfinder. About the size of a large house cat, the six-wheeled, solar-powered Sojourner became the first successful Martian rover. Surrounding Pathfinder are deflated airbags and the rock-strewn terrain of the Ares Vallis floodplain. In the distance Martian hills appear against a dusty brownish sky. The Pathfinder lander was subsequently renamed the Carl Sagan Memorial Station.
via NASA APOD
Key facts
- Discovered by
- Friedrich Tietjen
- Discovery date
- January 4, 1866
- Pronunciation
- / ˈ s ɛ m ɪ l ə /
- Named after
- Semele
- Minor planet category
- Main belt
- Adjectives
- Semelean / s ɛ m ɪ ˈ l eɪ ə n /
- Aphelion
- 562.652 million km (3.761 AU)
- Perihelion
- 369.116 million km (2.467 AU)
- Semi major axis
- 465.884 million km (3.114 AU )
- Orbital period sidereal
- 2,007.366 d (5.50 a )
- Average orbital speed
- 16.69 km/s
- Mean anomaly
- 264.875°
- Inclination
- 4.822°
- Longitude of ascending node
- 86.452°
- Argument of perihelion
- 307.886°
- Dimensions
- 120.6 km
- Mass
- 1.8 × 10 kg
- Equatorial surface gravity
- 0.0337 m/s²
via Wikipedia infobox
Wikidata facts
- Instance of
- asteroid
- Named after
- Semele
- Followed by
- 87 Sylvia
- Follows
- 85 Io
- Parent body
- Sun
- Minor-planet group
- asteroid belt
- Diameter
- 109.929
- Mass
- 1.8
- Orbital period
- 1999.513079344396
Show 21 more facts
- discoverer or inventor
- Friedrich Tietjen
- site of astronomical discovery
- Berlin Observatory
- provisional designation
- A866 AA
- time of discovery or invention
- 1866-01-04
- asteroid spectral type
- C-type asteroid
- orbital inclination
- 4.820781590521086
- density
- 2
- rotation period
- 16.634
- apparent magnitude
- 15.27
- albedo
- 0.056
- Commons category
- 86 Semele
- absolute magnitude
- 8.7
- orbital eccentricity
- 0.2176916750823394
- semi-major axis of an orbit
- 3.106112740404119
- periapsis
- 2.429937854950951
- apoapsis
- 3.782287625857288
- longitude of ascending node
- 86.06219295779552
- argument of periapsis
- 308.9345521077692
- mean anomaly
- 63.96395906035136
- time of periapsis
- 2460645.231186812
- epoch
- November 21, 2025
Sources (2)
via Wikidata · CC0
~1 min read
Encyclopedic overview
86 Semele is a large and very dark main-belt asteroid with an orbital period of 5.5 years. It is rotating with a period of 16.6 hours, and varies in magnitude by 0.13 during each cycle. This object is classified as a C-type asteroid and is probably composed of carbonates.
Semele was discovered by German astronomer Friedrich Tietjen on January 4, 1866. It was his first and only asteroid discovery. It is named after Semele, the mother of Dionysus in Greek mythology.
Excerpted from Wikipedia’s “86 Semele” article, available under the CC BY-SA 4.0 licence.