Editing Solar mass (section)

== Variation ==
The Sun is losing mass because of [[Nuclear fusion|fusion reactions]] occurring within its core, leading to the emission of [[Radiant energy|electromagnetic energy]], neutrinos and by the ejection of matter with the [[solar wind]]. It is expelling about {{Solar mass|{{val|2|-|3|e=-14}}}}/year.<ref name=carroll_ostlie1995>{{citation | first1=Bradley W. | last1=Carroll | last2=Ostlie | first2=Dale A. | date=1995 | title=An Introduction to Modern Astrophysics | edition=revised 2nd | publisher=Benjamin Cummings | isbn=0201547309 | page=409 | postscript=. }}</ref> The mass loss rate will increase when the Sun enters the [[red giant]] stage, climbing to {{Solar mass|{{val|7|-|9|e=-14}}}}/year when it reaches the [[tip of the red-giant branch]]. This will rise to {{Solar mass|{{10^|-6}}}}/year on the [[asymptotic giant branch]], before peaking at a rate of 10<sup>−5</sup> to 10<sup>−4</sup> {{Solar mass}}/year as the Sun generates a [[planetary nebula]]. By the time the Sun becomes a degenerate [[white dwarf]], it will have lost 46% of its starting mass.<ref name=mnras361>{{citation | last1=Schröder | first1=K.-P. | last2=Connon Smith | first2=Robert | s2cid=10073988 | title=Distant future of the Sun and Earth revisited | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=386 | issue=1 | pages=155–163 | doi=10.1111/j.1365-2966.2008.13022.x | date=2008 | doi-access=free | bibcode=2008MNRAS.386..155S|arxiv = 0801.4031 }}</ref>

The mass of the Sun has been decreasing since the time it formed. This occurs through two processes in nearly equal amounts. First, in the [[Solar core|Sun's core]], hydrogen is converted into helium through [[nuclear fusion]], in particular the [[proton–proton chain|p–p chain]], and this reaction converts some mass into energy in the form of [[gamma ray]] photons. Most of this energy eventually [[Solar luminosity|radiates away]] from the Sun. Second, high-energy protons and electrons in the atmosphere of the Sun are ejected directly into outer space as the [[solar wind]] and [[coronal mass ejection]]s.<ref>{{cite journal |last1=Genova |first1=Antonio |last2=Mazarico |first2=Erwan |last3=Goossens |first3=Sander |last4=Lemoine |first4=Frank G. |last5=Neumann |first5=Gregory A. |last6=Smith |first6=David E. |last7=Zuber |first7=Maria T. |title=Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission |journal=Nature Communications |date=18 January 2018 |volume=9 |issue=1 |pages=289 |doi=10.1038/s41467-017-02558-1 |language=en |issn=2041-1723 |quote=The fusion cycle that generates energy into the Sun relies on the conversion of hydrogen into helium, which is responsible for a solar mass reduction with a rate of ~&nbsp;−0.67&nbsp;×&nbsp;10<sup>−13</sup> per year. On the other hand, the solar wind contribution is more uncertain. The solar cycle significantly influences the solar mass loss rate due to solar wind. Estimates of the mass carried away with the solar wind showed rates between −&nbsp;(2–3)&nbsp;×&nbsp;10<sup>−14</sup>{{solar mass}} per year, whereas numerical simulations of coupled corona and solar wind models provided rates between −&nbsp;(4.2–6.9)&nbsp;×&nbsp;10<sup>−14</sup>&nbsp;{{solar mass}} per year.|doi-access=free |pmid=29348613 |pmc=5773540 |bibcode=2018NatCo...9..289G }}</ref>

The original mass of the Sun at the time it reached the [[main sequence]] remains uncertain.<ref>{{Cite web|title=Lecture 40: The Once and Future Sun|url=http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit6/futuresun.html|access-date=2020-09-01|website=www.astronomy.ohio-state.edu}}</ref> The early Sun had much higher mass-loss rates than at present, and it may have lost anywhere from 1–7% of its natal mass over the course of its main-sequence lifetime.<ref name=apj583_2_1024/> <!--The Sun gains a very small amount of mass through the impact of [[asteroid]]s and [[comet]]s.-->