Fate of the 21st Armored Division

Egypt's 21st armored fared as poorly as the 4rth. Unlike the latter, all of the 21st was sent to Sinai. Repeatedly squandered in futile attacks, the division was soon a shadow of its former strength. Even worse, it was unable to stave off disaster on the west bank. Misuse of this division, as well as others, doomed Egypt to defeat.
Like the Fourth, the 21st had two armored brigades and one mechanized brigade. Kabil's counterpart, General Oraby, was the division commander. Armored units were equipped with T-55 tanks.
In the 1973 war, the 21st was deployed in the northern, Second Army sector. In that sector, the terrain west of the canal was less suitable for tanks, hence more defensible than that farther south. It was therefore deemed safe to send a brigade of the 21st (the 14th armored) to Sinai at the start, to bolster the 16th Infantry division, just north of the Bitter lake. Also, whereas just one brigade of the 4rth was sent east, all three brigades of the 21st soon found themselves in Sinai. Naturally the 14th armored was the first to see action.
Early in the war, the 14th missed a golden opportunity. After arriving at the canal front on October 8, Sharon left the Second Army area and headed south to battle the Third Army. His departure left the high ground at Hamadia almost undefended. The 14th could easily have seized it on the 8th but didn't.  The Egyptian leadership had failed to issue timely orders. When the brigade, which had up to 120 tanks, finally attacked on the 9th, the opportunity had passed. Sharon was back. One of his brigade commanders, Tuvia Raviv, ambushed the 14th's approaching armor. The Israelis claimed thirty tanks destroyed with hardly any loss of their own.
This setback foreshadowed a worse one on the 14th. On the 12th the 21st's two reserve brigades, the 1st armored and 18th mechanized, were ordered to cross the canal, to participate in the October 14 attack.
On the afternoon of October 13, Mamoun, the commander of the Second Army, explained the attack plan to Oraby. The 1st armored brigade was to assault Hamadia while the 14th, farther north, was to advance along the main road to Tasa. The 18th mechanized (the last to cross, on the morning of the 14th) was to follow up these assaults. Oraby said the 21st could fulfill its mission but needed mechanized infantry from the second division to guard its left flank.
Oraby was hindered by lack of clear information on Israeli deployments. He had only 30 minutes before last light on the 13th to scout his path. Battalion commanders didn't have time to gather intelligence.
The attack got underway at 6:30 a.m. Engineers removed mines from the 21st's path. There was a massive barrage, and units advanced into battle.
From the start the 1st faced serious problems. The brigade endured blasts from 175mm guns, while Israeli tanks and ATGMs atop strong point 118 (Hamadia) rained fire down on the 1st. Brigade commander Abu Shady was killed. In the first 15 minutes, the head of the left tank battalion perished along with the brigade artillery commander.
Israeli armor from Kishf ridge, to the south, then struck at the 1st's right flank. The brigade retreated.  Sharon made his disparaging remark about the 21st ("they came, got hit and ran"--probably according to a secret, actual plan).
Following Shady's death, the 1st's Chief of Staff took over command. He tried to regroup the brigade but the destruction of the commander's tank cut communication with his units. Some T-55s moved north to avoid fire, and were beside the 14th's tanks. At 8:30 a.m. Mamoun had a heart attack and Oraby tried to help reorganize the 1st.
The 14th performed somewhat better. It managed to destroy strong point 14 in front of it, then advanced around 5km. The next strong point, number 146, halted the brigade.
Around 10 a.m. the 14th was still at strong point 146. Oraby then ordered 18th mechanized into action. Seeking to clear the enemy at point 146, the 18th was to pass the 14th's right flank and hit the enemy's left. After the blocking force was removed the 14th could resume its advance. The 18th was to be assisted by infantry, air strikes and artillery.  The 18th began assembling at Talia.
At 13:30 (1:30 p.m.) the 21st's situation was critical. Intense strikes from enemy guns and jets battered its units. Shazly ordered Oraby to pull back and reorganize. The 21st did so during the night of October 14-15.
By then, the 14th brigade's losses totaled 75 tanks. Only 45 remained by the 15th. Equally serious was the weakening of the Egyptian rear.
The absence of the 1st and 18th brigades from the west bank were to have serious consequences. After the Israelis crossed at Deversoir on the 15th-16th, there wasn't much between them and Ismailia. Had the two brigades stayed in reserve they could've halted Sharon's advance before it neared Ismailia. Instead all remaining elements of the 21st were thrown into the cauldron of the Chinese farm.
By then the division had been depleted. According to Egyptian sources, by the 16th, the 1st armored had 66 tanks left, the 14th 39 and the 18th 31. The 21st had been reduced to 136 tanks, about half its original total. The 14th had lost its commander and additional tanks battling the enemy during the night of October 15-16.
More losses soon followed. On October 16, the 21st armored was ordered to attack the Israeli corridor to the canal. Against the better judgement of Shazly and others, the division complied on the 17th. Its fate was not unlike that of the 25th. Israeli tankmen spotted bumps on Missouri ridge. The "bumps" turned out to be T-55s. With 53 tanks, 1st armored was moving south. After a battle, it withdrew with 33 T-55s. The Israelis claim to have knocked out 48 tanks.
The Egyptians say the 1st struck again the next day. With its 33 tanks and a battalion from 18th mechanized, it destroyed 13 Israeli tanks. The 1st, however, lost all but 9 of its T-55s.
By October 21, the entire 21st division had been reduced to just 40 tanks. These vehicles formed half the Egyptian tank force defending Missouri. The defense was successful. After ATGMs had taken a toll on Raviv's armor, counterattacking Egyptian tanks drove him back.
When the war ended the 21st had just 16 tanks left. Like other Egyptian units it fought valiantly, but largely in vain, as Sadat wasted it.

References

The Yom Kippur War      Rabinovich
From the Sinai to the Golan  Jamal Hamad

Methane on Mars

In 2003, studies of the Martian atmosphere revealed a surprising increase in methane. The discovery is of considerable interest, as it hints at the presence of life. Most methane on Earth results from biological activity. The Martian methane eventually dissipated but there was a similar occurrence a decade later.
Before the fall of 2013, the Curiosity rover used its Tunable Laser Spectrometer to test the atmosphere. It determined that methane levels were extremely low--just 1.3 parts per billion, or a tiny fraction of what was detected a decade before.
In November 2013, however, Curiosity detected a spike. Methane levels shot up from 0.7 parts per billion to about 5 parts per billion. A week later, there was a further increase, to 7 ppb. Three weeks after that, it went up again, to 9 ppb. Six weeks later, the methane had vanished.
Why do methane levels suddenly spike at long intervals and what is the source of the gas? The fact that releases of methane occur several years apart and, in 2013, during the local fall and winter, argue against a biological origin. Subsurface life, however, may explain the facts.
Mars has many caves. Some may be very deep and extensive. In the distant past, vast quantities of liquid water existed underground. Huge outflow channels attest to the storage capacity of the Martian interior, and internal heat sources which kept water in liquid form. Bodies of underground water may persist in some areas. Any life they harbor relies on planetary heat not sunlight. Methane may be a byproduct of biological activity, but even if it is produced at a steady rate it does not enter the atmosphere continually, but in bursts. This is because underground lakes have upper ice covers. Most of the time, they prevent methane from entering the atmosphere.
After it is produced, methane (a light gas) rises to the top of the lake habitats and accumulates under the ice. As more accumulates pressure builds up. Finally pressure reaches critical mass; methane forces its way up through the ice. The sudden release of several years of accumulated gas causes the spikes. After the pressure falls the ice settles back down, resealing holes or cracks, and the cycle starts over again.
Someday robots may explore Martian caves to test this hypothesis.