Venus

Venus may have had a shallow liquid-water ocean and habitable surface temperatures for up to 2 billion years of its early history, according to computer modeling of the planet’s ancient climate by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York.

 Second planet from the Sun and our closest planetary neighbor, Venus is similar in structure and size to Earth, but it is now a very different world. Venus spins slowly in the opposite direction most planets do. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system—with surface temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains.

10 Things to Know About Venus

1

EARTH-SIZED

If the sun were as tall as a typical front door, the Earth and Venus would each be about the size of a nickel.  

2

SECOND ROCK

Venus orbits our Sun, a star. Venus is the second closest planet to the sun at a distance of about 67 million miles (108 million km).

3

A DAY LONGER THAN A YEAR

One day on Venus lasts 243 Earth days because Venus spins backwards, with its sun rising in the west and setting in the east.HASING CLOUDS ON VENUS

4

DIVERSE TERRAIN

Venus' solid surface is a volcanic landscape covered with extensive plains featuring high volcanic mountains and vast ridged plateaus.

5

MOONLESS AND RINGLESS

Venus has no moons and no rings.

6

GREENHOUSE EFFECT

The planet’s surface temperature is about 900 degrees Fahrenheit (465 degrees Celsius)—hot enough to melt lead.

7

WATER ON VENUS

Many scientists believe water once existed on the surface. Future Venus explorers will search for evidence of an ancient ocean.

8

MANY VISITORS

More than 40 spacecraft have explored Venus. The ‘90s Magellan mission mapped the planet's surface and Akatsuki is currently orbiting Venus.

9

LIFE ON VENUS

Venus’ extreme temperatures and acidic clouds make it an unlikely place for life as we know it.

10

SUPER ROTATING ATMOSPHERE

While the surface rotates slowly, the winds blow at hurricane force, sending clouds completely around the planet every five days.

Mercury

Like the waistband of a couch potato in midlife, the orbits of planets in our solar system are expanding. It happens because the Sun’s gravitational grip gradually weakens as our star ages and loses mass. Recently, a team of NASA and MIT scientists indirectly measured the Sun's mass loss and other solar parameters by looking at changes in Mercury’s orbit.

 The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's moon. From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as 11 times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system—that title belongs to nearby Venus—but it is the fastest, zipping around the Sun every 88 Earth days.

10 Things to Know About Mercury

1

SMALLEST

Mercury is the smallest planet in our solar system - only slightly larger than the Earth's moon. If the sun were as tall as a typical front door, Earth would be the size of a nickel and Mercury would be about as big as a green pea.

2

INSIDER

It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.

3

LONG DAYS, SHORT YEARS

One day on Mercury (the time it takes for Mercury to rotate or spin once with respect to the stars) takes 59 Earth days. One day-night cycle on Mercury takes 175.97 Earth days. Mercury makes a complete orbit around the sun (a year in Mercury time) in just 88 Earth days.

4

ROUGH SURFACE

Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like the Earth's moon.

5

CAN'T BREATHE IT

Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere.

6

MOONLESS

Mercury has no moons. 

7

RINGLESS

There are no rings around Mercury. 

8

TOUGH PLACE TO LIVE

No evidence for life has been found on Mercury. Daytime Temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to -180 degrees Celsius (-290 degrees Fahrenheit) at night. It is unlikely life (as we know it) could survive on this planet.

9

BIG SUN

Standing on Mercury's surface at its closest point to the sun, the sun would appear more than three times larger than it does on Earth.

10

ROBOTIC VISITORS

Only two missions have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.

The Solar System

The Solar System^[a] is the gravitationallybound system comprising the Sun and the objects that orbit it, either directly or indirectly.^[b] Of those objects that orbit the Sun directly, the largest eight are the planets,^[c] with the remainder being smaller objects, such as dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.^[d]

Solar System

The Sun and planets of the Solar System (distances not to scale)
Age	4.568 billion years
Location	Local Interstellar Cloud, Local Bubble, Orion–Cygnus Arm, Milky Way
System mass	1.0014 Solar masses
Nearest star	Proxima Centauri  (4.22ly) Alpha Centauri (4.37 ly)
Nearest knownplanetary system	Proxima Centaurisystem  (4.25 ly)
Semi-major axis of outer known planet (Neptune)	30.10 AU  (4.503 billion km)
Distance to Kuiper cliff	50 AU
Populations
Stars	1  (Sun)
Known planets	8 (Mercury   Venus   Earth   Mars   Jupiter   Saturn   Uranus   Neptune)
Known dwarf planets	Possibly several hundred;[1] five currently recognized by the IAU (Ceres   Pluto   Haumea   Makemake   Eris)
Known natural satellites	472 (175 planetary[2]   297 minor planetary[3])
Known minor planets	707,664  (as of 2016-03-07)[4]
Known comets	3,406  (as of 2016-03-07)[4]
Identified rounded satellites	19
Invariable-to-galactic plane inclination	60.19°  (ecliptic)
Distance to Galactic Center	27,000 ± 1,000 ly
Orbital speed	220 km/s
Orbital period	225–250 Myr
Spectral type	G2V
Frost line	≈5 AU[5]
Distance to heliopause	≈120 AU
Hill sphere radius	≈1–3 ly

The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

The Solar System also contains smaller objects.^[e] The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity.^[10] Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris.^[e] In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, at least four of the dwarf planets, and many of the smaller bodies are orbited by natural satellites,^[f] usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar mediumknown as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way.