- Origin of name: Venus is the
bright "Morning Star" or "Evening Star",
and was sometimes given two different names [like Phosphoros
and Hesperus]; Associated with the goddess of love and beauty,
Venus (Romans), Aphrodite (Greeks), Ishtar (Babylonians).
- View from Earth: [So bright it sometimes
casts shadows!] Even with a telescope it looks smooth and featureless,
from total cloud cover;
It shows no moons* or rings.
- Rotation and revolution: The
rotation (first measured by bouncing radio waves off the surface)
is slow and retrograde [with 243-day period], probably due to
a past collision or friction between the atmosphere and the planet;
The orbit is almost circular at 0.72 AU [225-day period].
- Days and years: Because of the
slow retrograde rotation, the solar day on Venus is much shorter
than the sidereal one [116.8 Earth days long, compared to 243],
and the Venus year is a little less than 2 Venus days!
- Early missions: 1962-1974, NASA's Mariner
series flybys; 1970s and 1980s, The Soviet Venera series landers (the first landing
by spacecraft from Earth on another planet), which sent us the
first photographs of the surface; Pioneer Venus (Probe
1978, Orbiter 1978-1982).
- More recent: 1989-1994, Magellan orbiter; No
active spacecraft near the planet since then, but the ESA launched
the Venus Express mission in November 2005, and it is now in orbit around
Venus; The ESA and Japan are planning missions.
- View from orbit: UV satellite
images show cloud patterns and winds; To map the surface features
we must use radio waves.
- Size: The radius is 95% of Earth's,
and the density similar to Earth's [mass 80%] (How do we know what
the mass is?).
- Core: It is believed that Venus
has a liquid metal core similar to the Earth's, and we have no
seismic data to confirm this, but no magnetic field has been
found (possibly because of the planet's slow rotation).
- Activity: There is some evidence
for plate tectonics and volcanism, but not on the same scale
as on Earth; The absence of old craters may indicate that the
planet behaves like a pressure cooker which occasionally explodes
on a global scale, rather than gradually releasing heat; The
high temperature may make the crust hotter and lighter than Earth's.
Exterior and Surface
- Atmosphere: Thick, high pressure
(90 atm near the surface, and a density 50 times greater than
on Earth! Why?), made of CO2,
N, with sulfuric acid clouds; Protects the surface against solar
wind; Produces a strong greenhouse effect, but little erosion,
because there is not much rain or surface wind.
- Surface: It is 450°C (850°F)
hot everywhere, always (including nighttime), because the atmosphere
traps heat very effectively; Dry, of dusty rocks, with no water
(it is too hot, but it may have had water in the past); Illuminated
as much as the Earth's on an overcast day by orange light, because
- Features: Radio maps show mountains,
rolling plains, riverbeds, coronas, and some craters (from volcanoes
and impacts, but no old ones or small ones, in part because small meteoroids
break up in the atmosphere); But the surface is less rugged than Earth's,
young and all the same age; We think that Venus was totally resurfaced
600-700 million years ago; There
are cracks produced by temperature changes.
page by luca bombelli <bombelli at olemiss.edu>,
modified 7 oct 2013
* Curiosities: Neith, the mysterious goddess of Sais, whose
veil no mortal raised
In 1672, Giovanni Domenico Cassini, one of the prominent astronomers
of the time, noticed a small companion close to Venus. Later,
the object was seen by other astronomers as well. Most observations
of the satellite were really stars seen in the vicinity of Venus.
Aug 13, 1892: E. E. Barnard recorded a 7th magnitude object
near Venus. There is no star in the position recorded by Barnard,
and Barnard's eyesight was notoriously excellent. We still don't
know what he saw. Was it an asteroid that hadn't been charted?
Or was it a short-lived nova that nobody else happened to see?