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The "standard" Morava E-theory $E_n$ (at a prime $p$) is typically defined using the so-called "Honda formal group law", the unique FGL $\Gamma_n$ over $\mathbb{F}_{p^n}$ satisfying $[p]_{\Gamma_n}x=x^{p^n}$. The story is that we take the universal deformation of $\Gamma_n$, which is Landweber exact, and lift it to a complex-oriented $E_{\infty}$-ring with an action of the Morava stabilizer group $\mathbb{G}_n=\operatorname{Aut}_{\mathbb{F}_{p^n}}(\Gamma_n)\rtimes\operatorname{Gal}(\mathbb{F}_{p^n}/\mathbb{F}_p)$. Then this is a pro-Galois extension of $L_{K(n)}\mathbb{S}$ with Galois group $\mathbb{G}_n$, and we can use this to obtain a fixed-point spectral sequence and so on.

Except...the Honda FGL is not unique in this regard. Given any formal group of height exactly $n$, its universal deformation will yield a presentation for the formal neighborhood of the height $n$ formal groups in $\mathcal{M}_{fg}$, and we'll get an associated pro-Galois extension and an equivalent fixed-point spectral sequence. The multiplicative structure on the Lubin-Tate spectrum will be different and we'll get a different description of the $E_1$ page of the FPSS, but ultimately this just yields a different presentation of the same object (the $K(n)$-local sphere).

So, why do we use the Honda formal group? Is it for historical reasons? Is it for computational convenience? Or is there something deeper going on with the Frobenius map? I was until recently laboring under the misapprehension that there was something pertinently "universal" about this formal group, but now I'm wondering if there's any reason not to replace it with some other one (e.g. a supersingular elliptic curve at height $2$).

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    $\begingroup$ My understanding largely agrees with yours: in homotopy theory, the choice of the Honda FGL over others mostly doesn’t matter, though it can be convenient when making computational arguments which pass to the residue field. Though how much you care depends on your aims, the situation is different in number theory: Lubin and Tate really did want particular behavior at the residue field, where any old formal group law would not do, and reasons have been found to look at particular deformations over others as well. “Quasicanonical lift” is a good keyword to search. $\endgroup$ Commented Feb 5, 2023 at 1:13
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    $\begingroup$ I meant also to mention this paper by Chatham, Hahn, and Yuan (arxiv.org/abs/1910.04616), where they investigate various orientations for various E-theories and find some instances where the choice of formal group matters. This is a different direction one could take your question: in advance of passing to an “invariant” object like L_K(n) S, one can make queries of the different E-theories themselves and get qualitatively different answers. $\endgroup$ Commented Feb 6, 2023 at 6:18

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