January 4

4 January 1643

Portrait of Isaac Newton by Godfrey Kneller. Oil on canvas, 1689

Isaac Newton, one of the greatest mathematicians and physicists of all time, was born on January 4, 1643, New Style (December 25, 1642, Old Style) in Woolsthorpe, Lincolnshire, England.

After a grammar school education in Grantham, Newton entered Trinity College, Cambridge, in June 1661 and was chosen as a scholar in 1664. In 1669, the college elected him a fellow and, in 1669, the university appointed him Lucasian Professor of Geometry. In 1696, he moved to London to become Warden of the Mint, then Master of the Mint in late 1699; he resigned his Trinity College fellowship and professorial chair in 1701. In 1703 he was elected President of the Royal Society. He died on March 31, 1727, New Style (March 20, 1726, Old Style) in London.

Newton was a key figure in the Scientific Revolution of the 17th century. In his work Philosophiæ Naturalis Principia Mathematica, published in 1687 (later editions in 1713 and 1726), he established the foundations of classical mechanics, including the three laws of motion and the law of universal gravitation. The Principia transformed physical science and is considered one of the most important works in the history of science. In Opticks (editions 1704 and 1717), Newton wrote about the nature of light and described the heterogeneity of white light. In mathematics he developed binomial theorem and fundamental theorem of the calculus. He is also the inventor of the first practical reflecting telescope, completed in early 1669.

Replica of Newton's first reflecting telescope made in 1668 and now in the possession of the Royal Society of London. Replica was made for the Science Museum in 1924 by Mr F.L. Agate

The three laws of motion describe the relations between the forces acting on a body and the motion of the body. They were first stated by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica:

1. A body remains at rest, or in motion at a constant speed in a straight line, unless it is acted upon by a force.

2. At any instant of time, the net force on a body is equal to the body's acceleration multiplied by its mass or, equivalently, the rate at which the body's momentum is changing with time:

F = ma = dp/dt

3. If two bodies exert forces on each other, these forces have the same magnitude but opposite directions.

Newton's law of universal gravitation describes gravity as a force:

Any particle of matter in the universe attracts any other with a force varying directly as the product of the masses and inversely as the square of the distance between them.

F = G(m₁m₂)/R²

where F is the gravitational force acting between two objects, m₁ and m₂ are the masses of the objects, R is the distance between the centers of mass, and G is the gravitational constant.

Portrait of Sir Isaac Newton by Godfrey Kneller. Oil on Canvas, 1702. National Portrait Gallery

See also: Galileo Galilei, James Clerk Maxwell, Albert Einstein

4 January 2004

Artist's illustration of NASA's Spirit Mars rover shortly after its January 4, 2004 landing. Credit: NASA/JPL-Caltech

On January 4, 2004, Mars Exploration Rover – A (Spirit or MER-2) landed in the Gusev crater on the surface of Mars, embarking on a more than 6-year mission. The total distance driven by the rover was 7,730.50 meters, and the last communication with it was established on March 22, 2010.

Spirit was one of two rovers of NASA's Mars Exploration Rover Mission managed by the Jet Propulsion Laboratory (JPL). The scientific objectives of the Mars Exploration Rover mission were to:

1) search for and characterize a variety of rocks and soils that hold clues to past water activity,

2) determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites, 3) determine what geologic processes have shaped the local terrain and influenced the chemistry,

4) perform "ground truth" of surface observations made by Mars orbiter instruments,

5) search for iron-bearing minerals, identify and quantify relative amounts of specific mineral types that contain water or were formed in water,

6) characterize the mineralogy and textures of rocks and soils and determine the processes that created them, and

7) search for geological clues to the environmental conditions that existed when liquid water was present and assess whether those environments were conducive to life.

The rover carried a suite of instruments for science and navigation. The panoramic camera (Pancam) and navigation cameras were mounted on top of the Pancam mast assembly, at a height of about 1.4 meters from the base of the wheels. The mast, mounted at the front of the equipment deck, also acted as a periscope for the Miniature Thermal Emission Spectrometer (Mini-TES). Attached to the end of the instrument deployment device were the Alpha Particle X-Ray Spectrometer (APXS), Mossbauer Spectrometer (MB), Microscopic Imager (MI), and Rock Abrasion Tool (RAT). A magnet array was attached to the front of the equipment deck. Two hazard avoidance cameras were mounted on the front of the rover and two on the rear. The group of science instruments (Pancam, Mini-TES, APXS, MB, MI, and RAT) is known as the Athena science package. The rover had a mass of 185 kilograms.

Spirit was launched on a standard Delta II 7925 on June 10, 2003. The cruise phase to Mars ended on November 20, 2003, 45 days before Mars entry. The approach phase lasted from this date until martian atmospheric entry on January 4, 2004. On entry the lander and components had a mass of 827 kg and were travelling at 19,300 km/h. The aeroshell decelerated the lander in the upper martian atmosphere for about four minutes to a velocity of 1600 km/h, followed by deployment of a parachute. The parachute slowed the spacecraft to about 300 km/h. A series of tones was transmitted by the spacecraft during entry and after landing to indicate the successful completion of each phase. Just prior to impact, at an altitude of about 100 m, retrorockets slowed the descent and airbags were inflated to cushion the impact. The craft hit at roughly 50 km/h and bounced and rolled along the surface. It bounced a total of 28 times before rolling to a stop about 250–300 meters from point of first impact. After it stopped the airbags deflated and retracted, the petals opened, and the rover deployed its solar arrays.

Artist's concept of inflated airbags, used by Mars Exploration Rover, at the moment of landing. Credit: NASA/JPL

This image mosaic taken by the panoramic camera onboard the Mars Exploration Rover Spirit shows the rover's landing site, the Columbia Memorial Station, at Gusev Crater, Mars. This spectacular view may encapsulate Spirit's entire journey, from lander to its possible final destination toward the east hills. On its way, the rover will travel 250 meters northeast to a large crater approximately 200 meters across, the ridge of which can be seen to the left of this image. To the right are the east hills, about 3 kilometers away from the lander. The picture was taken on the 16th martian day, or sol, of the mission (Jan. 18/19, 2004). A portion of Spirit's solar panels appear in the foreground. Data from the panoramic camera's green, blue and infrared filters were combined to create this approximate true color image. Credit: NASA/JPL

The landing took place at 04:35 UT on January 4, 2004, in Gusev Crater, at 14.5692° S, 175.4729° E,. About three hours after landing the first images were returned to Earth, showing a flat plain littered with small rocks. Gusev Crater was chosen as a landing site because it has the appearance of a crater lakebed. If Gusev was at one time filled with water, the bottom of the crater may contain sedimentary deposits laid down in the submarine environment.

An egress phase took place over the first few days, involving deployment of the Pancam mast and high gain antenna, rover stand up, imaging and calibration, and selection of proper egress path. The rover drove off the platform onto the surface of Mars on January 15 at 8:41 UT. The rover ran into a major problem on January 21, 2004 when NASA’s Deep Space Network lost contact. Due to a problem in Spirit’s flash memory subsystem, the rover entered a “fault mode.” Fortunately, controllers were able to reformat the flash memory and send up a software patch (to preclude memory overload). Normal operations resumed again on February 5. The rover explored Gusev crater, taking images and making scientific measurements, although it lost the use of one of its six wheels.

The sunset on Mars seen on May 19, 2005. Credit: NASA/JPL-Caltech/Cornell Univ.

By 2005, the rover began slowly making its way uphill to the apex of Husband Hill, over terrain that was both rocky and sandy. It stopped at many locations to investigate, often using the RAT. In March 2005, a peculiar and strange event, the passing of dust devils that swept dust from the top of the solar panels, increased power coming to Spirit from the usual 60% to 93%, thus significantly extending the lifetime of the mission. On September 29, 2005, the rover finally reached the summit of Husband Hill, a small flat plain, from which Spirit was able to take 360° panoramas in real color of the Gusev Crater.

On April 23, 2009, the rover broke through a thin crust into a pocket of sand that severely limited its mobility. By May 1, 2009, it could no longer move at all. Numerous attempts to move the rover were unsuccessful, and the solar panels could not be oriented in a direction to produce enough power to make it through the winter. The last transmission from Spirit occurred on March 22, 2010. The rover returned 128,224 raw images, and travelled a total of 7.73 km over a period of 6 years, 2 months, and 19 days, more than 25 times its original intended lifetime.