Question

Read the articles on the Pioneer spacecraft anomaly. How does this affect Newton's law of universal gravitation? Do you think the researchers' hypothesis that the gravitational constant may be changing was reasonable, especially as it relates to the Scientific Method?

https://www.space.com/16648-pioneer-anomaly-spacecraft-mystery-solved.html

http://www.planetary.org/blogs/bruce-betts/3459.html

Answer 1

Pioneers 10 and 11 were launched in the 1970’s ,by the basic knowledge as they traveled away from the Sun, they slowed down

Most of this slowing was expected by simple physics laws a result of the gravitational pull of the Sun and other massive objects in the solar system but when everything in the solar system whose mass could have any effect on the Pioneers was accounted for both spacecraft were found to slowing more than expected. The excess slowing was very small but measurable

Here question arises that why was the thermal emission from the spacecraft anisotropic and slowing the spacecraft down.Because the Pioneer spacecraft were spin-stabilized and almost always pointed their big dishes towards Earth and two sources of thermal radiation were then on the leading side of the spacecraft. The nuclear power sources, more formally Radioisotope Thermoelectric Generators emitted heat towards the back side of the dishes and when the dishes reflected or re-radiated this heat it went in the direction of travel of the spacecraft.It is accounted that the warm electronics box for the spacecraft was on the leading side of the spacecraft, causing more heat to spill that direction. Photon pressure, the same type of thing used in solar sailing, then preferentially pushed against the direction of travel, causing a tiny, but measurable, deceleration of the spacecraft – the Pioneer Anomaly

As a matter of fact gravity didn't seem to be working right for the Pioneers.

we realized that the universe accelerates because of this dark energy and people were ecstatic saying that look we see something very exciting in the solar system and maybe we need to modify gravity and all of that will go away and Einstein and Newton may be

This review begins with two historical stories anecdotes of obvious pertinence ,one is the anomalous precession of Mercury's perihelion the seed that 59 years later developed into Einstein's general relativity and the end of physics and second is a lesser-known tale of anomalous celestial motion.Here in 19th century, astronomers noticed that the distant planet Uranus had a funky orbitit deviated from the path prescribed for it by Newtonian gravity and Some prominent astronomers suggest that perhaps Newton's laws break down at great distances from the Sun. visualisation of that kind lasted until 1850 at which point another distant planet was discovered right where it needed to perturb the orbit of Uranus in a way it was perturbed and that planet was Neptune and Newton's law was safe again.